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Animal breeding course

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Animal breeding course

  1. 1. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 1 UNIERSITY OF HARGEISA COLLEGE OF AGRICULTURE, VETERINARY AND ANIMAL SCEINCE Faculty of Animal science Program Faculty Animal Science Courses Title Animal breeding Pre-requisites Animal genetics Instructor Abdirahman Awsamire (MSc.) Course Description The scope of this course includes Historical development and modern concepts of animal breeding. Breeds of livestock and major traits in farm animals; Genetic parameters: heritability, repeatability, and correlation among traits. Categories of relationships; Principles and methods of selection (Selection based on records of individuals, progeny, pedigree, collateral relatives and combination of records simple selection indices). Mating systems in farm animals; Recording and standardization of herd records; Breeding programs in the tropics and their results; Development of new breeds; Principle of nucleus breeding program; Conservation of farm animal genetic resources: Course objective At the end of the course, the student will be able to: Describe the historical development and modern concept of animal breeding Identify and characterize the different breeds of livestock breeds Understand how to estimate genetic parameters Describe the categories of relationship and evaluate coefficients of relationship and inbreeding
  2. 2. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 2 Understand the principles of nucleus breeding program Identify methods of animal genetic conservation Understand the principles, types and methods of selection Describe the nature, opportunities and threats of animal breeding in the tropics
  3. 3. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 3 ANIMAL BEERING COURSE 1. INTRODUCTION Animal breeding is the application of principle of Genetics and Physiology of Reproduction for improvement of the animals. Improvement is betterment of the characters both qualitative and quantitative over those of the ancestors, over that of the average of family. Animal breed: breed is group of livestock (animals) with in the species of common origin. They have certain distinguishing characters not found in members of other group in the same species. These characters are transmitted to successive generation. Breeder: Breeder is one who planned and determined the type of mating. For practical purpose breeder of an animal is a person who owned the dam of that animal at the time of breeding (horse race course term). Task of animal breeder: The task of animal breeder is to speed up and control every process of improvement. A progressive breeder should bring about new combination of genes which are best suited to his purpose than the existing combinations. Hence he has to learn. 1. Probable genetic make up of his animals through a. Animals individualities b. Parentage c. Performance of their close relatives 2. Combining the favourable characters by a) Selection b) Breeding History of Animal Breeding Exact date as to when animal breeding was practised is not available from history. The evidences gathered from the archaeological excavations indicate that the Mediterranean countries (Egypt, Rome Greece) initiated the animal breeding. Egypt and Arabs are known for the horse breeding. Arabs in 12th century considered that dam was important in breeding and not aware of importance of the sire. At about the same time in Denmark and Holland the cattle breeding was practised by providing better environment such as feed. In U.K; the royal families in 14th century considered performance of horses for selection and breeding. The Earls and Dukes took interest in cattle breeding and imported the cattle from Denmark and Holland. Until the 18th century there was no planned or systematic animal breeding. During industrial revolution in England (1760) the people started migration from villages to cities. This created a heavy demanded for milk and meat. Robert
  4. 4. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 4 Bake well (1725-1790) an English man is generally acknowledged as great pioneer in Animal Breeding and father of Animal Breeding. Bake wells contributions and methods: 1. He had definite ideas, such as beef cattle should be low set, blocky, and quick maturing. 2. He gave more importance to sires by selecting best animals. 3. He started a systematic progeny testing of sires. He lent the good sires to other breeders for given fee and also insisted that the progeny of the sire should be rared under similar conditions. He used those males which gave the best progeny in his farm. 4. While breeding best to best he practised inbreeding which led to development of true breeding stock. 5. He also kept the records of individuals. In 18th century pure breeding was preferred and people wanted information on pure bred animals. To supply authenticated information one Mr. George Coat in 1822 opened the Herd Book for Short Horn cattle. It was followed by opening of Herd books for most of the breeds by middle of 19th century. The first association of farmers for milk recording was formed in Denmark and followed by all other milk producing countries. Modern History of Animal Breeding BREEDING ANIMALS AGRISCIENCE AND TECHNOLOGY TERMS USED IN BREEDING ANIMALS BREED: Breed is made up of animals of the same species that share common traits. BLOODLINES: Bloodlines are groups within breeds; tend to have one common ancestor. PUREBRED: Animals registered in a breed or eligible for registry. INHERIT TRAITS OF ANIMALS COLOR MILK CAPACITY HORNS SIZE TYPE
  5. 5. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 5 OFFSPRING THAT HAVE TRAITS GENETICALLY DIFFERENT FROM THEIR PARENTS ARE KNOWN AS MUTANTS. BREEDS OF CATTLE ANGUS: Originated in Scotland. Black, polled and have a smooth coat of hair. BRAHMAN: Originated in United States. Light gray to nearly black, loose skin and large humps over the shoulder; tolerant of heat and insects. BRANGUS: Developed by crossing Brahman and Angus cattle. Solid black and polled. CATTLE BREEDS CONT. CHAROLAIS: Originated in France. White to a light straw color; large breed, most are naturally horned. CHIANINA: Originated in Italy. White except for the switch of the tail, which is black; skin has a black pigment. Largest beef breed. HEREFORD: Originated in England. White face and red bodies. A horned breed. CATTLE BREEDS CONT. POLLED HEREFORD: Developed in the United States. White face and red bodies; polled. LIMOUSIN: Originated in France. Most are red but may be light yellow or black. They usually have horns. SANTA GERTRUDIS: Developed by the King Ranch in Texas. Cherry red, usually horned and have loose hide. Crosses of the Shorthorn and Brahman breeds. BEEF BREEDS CONT. SHORTHORN: Originated in England. Red and white, with a red-white mix (roan), have horns except for the Polled Shorthorn breed. SIMMENTAL: Originated in Switzerland. Faces are white/light straw and their bodies are red to dark red.
  6. 6. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 6 DAIRY CATTLE BREEDS AYRSHIRE: Originated in Scotland. Red, mahogany, brown or white in color. Rank third in milk production (11,700 lbs. per year with 4.0 % milk fat). BROWN SWISS: Originated in Switzerland. May be any shade of fawn with white markings. Rank fourth in milk production (10,600 lbs. per year with 5% milk fat). DAIRY BREEDS CONT. GUERNSEY: Originated off the coast of France. May be any shade of fawn with white markings; horns turn outward and toward the front. Tied for fourth in milk production (10,600 lbs. per year with 5% milk fat). HOLSTEIN: Originated in the Netherlands. Black and white color patterns. Rank first in milk production (14,500 lbs. per year with 3.5% milk fat). DAIRY BREEDS CONT. JERSEY: Originated on the Isle of Jersey. Color range from cream to almost black. Ranks fifth in milk production (10,000 lbs. per year with 5.4% milk fat). Smallest of the dairy breeds. SWINE BREEDS AMERICAN LANDRACE: White breed with ears drooped over the eyes. Produce large litters of pigs. BERKSHIRE: Black with six white points: each foot, some white on the face and a white tail switch; erect ears. CHESTER WHITE: White breed; popular in the northern parts of the United States. =
  7. 7. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 7 SHEEP BREEDS FINE WOOL SHEEP - Rambouillet, American Merino, Delaine Merino and Debouillet. MEDIUM WOOL SHEEP - Cheviot, Dorset, Finnish Landrace, Hampshire, Shropshire, Southdown and Suffolk. LONG WOOL SHEEP - Cotswold, Leicester, Lincoln and Romney. SHEEP BREEDS CONT. CROSSBRED WOOL SHEEP - Columbia, Panama and South dale. GOAT BREEDS MOHAIR AND CASHMERE - Angora; most of these are grown in Texas and other southwestern states. DAIRY GOATS - LaMancha, Nubian, Saanen and Toggenburg. POULTRY Poultry includes chickens, duck and turkey. Other poultry animals include quail, guinea, ostrich and emu. Most common breeds of chickens are White Leghorn, White Rock, Rhode Island Red, Barred Rock and New Hampshire. Chickens are selected for one of two uses: eggs and meat. AQUACULTURE Term used to describe the farming of fish. Examples include: catfish, trout, tilapia, hybrid striped bass, shrimp, oyster, crawfish, red fish, snails, crabs, alligators and frogs.
  8. 8. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 8 KINDS OF BREEDING SYSTEMS STRAIGHTBREEDING: Mating of animals of the same breed. Different approaches of straight breeding include purebred breeding (mating purebred animals), outcrossing (mating animals of the same breed but of different families in the breed) and inbreeding (mating animals of the same breed with closely related animals). BREEDING SYSTEMS CONT. CROSSBREEDING: Involves mating animals of different breeds. Used to improve the quality of the products yielded by the offspring. Used to produce calves with more meat, no horns or to accomplish other specific genetic purpose. PUREBRED PRODUCTION SYSTEM Used to produce purebred animals that will be used for meat, milk or other purposes. May compete in shows. Raise both male and female animals. Must keep accurate records. MEAT-ANIMAL PRODUCTION SYSTEM COW-CALF PRODUCTION - Involves keeping cows to produce calves that are used for meat. Calves are weaned at about 500 lbs.
  9. 9. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 9 METHODS OF INSEMINATING LIVESTOCK NATURAL INSEMINATINATION - Involves using animals to mate in pastures or pen breeding. ARTIFICIAL INSEMINATION - Involves collecting semen from a male and depositing it in the reproductive tract of the female. ADVANTAGES OF USING AI AI allows the use of semen from superior males that are owned by another party. AI makes it possible for a male to breed many more females than could be done naturally. * Semen can be stored for a week at 41F or for several months frozen at -320F (liquid nitrogen). IMPORTANT INFORMATION IN BREEDING ANIMALS SPECIES AGE/BREED GESTATION COW 14 MONTHS 283 DAYS SOW 12 MONTHS 114 DAYS EWE 17 MONTHS 148 DAYS DOE 18 MONTHS 151 DAYS MARE 2-3 YEARS 336 DAYS
  10. 10. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 10 ESTRUS SYNCHRONIZATION Involves using hormones to get several females to come in heat at the same time. Used when using advanced breeding procedures such as superovulation (getting the female to produce a number of eggs at one time) and embryo transfer. PREGNANCY TESTING BLOOD TEST URINE TEST RECTAL PALPATION (MOST COMMON METHOD USED) “BUMPING” SIGNS OF PREGNANT FEMALES GOING INTO LABOR ENLARGED UDDER SWELLING OF THE VULVA HOLLOWNESS IN FRONT OF THE PIN BONES NERVOUSNESS GOING AWAY FROM THE HERD GIVING BIRTH Most animals give birth without assistance. Calves should be born within one hour after labor begins. Calves are normally delivered with the head between the two front legs. Cow may need assistance if calf is in a different position. AFTER THE BIRTH It is very important that the calf gets the first milk known as “colostrum”. Colostrum is high in antibodies and other substances that help the new animal survive.
  11. 11. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 11 Animal should expel the placenta 3-6 hours after giving birth. 1.1. Breeding of Dairy Cattle 1.1.1. Selection Methods of Dairy Animals This selection is based on information available on the ancestors like parents, grandparents and great grandparents. The contribution beyond three generations is not much to be considered in pedigree selection. Pedigree selection enabled selection at an early age, and selection of males which do not express the traits like milk production through they transmit the genes for the traits. Individual Selection: Selection is based on the individuals own milk vein, teats, pelvic cavity and udder. This is ideal for characters with high heritability. Where as in dairy cattle most of the economic traits have low to moderate heritability. Family Selection: Where families are selected or rejected as units according to the phenotypic value of the family. The families may be full sibs or half sibs.~ The method is useful when the character for which selection is made has‟ low heritability. Two modifications of family selection applicable to dairy; cattle are sib selection and progeny testing.
  12. 12. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 12 Sib Selection: This is a type of a selection where in the selected individuals do not contribute to the family means. This applies to selection of males which do not express the characters and selection of females at an early age. Progeny Testing The criteria of selection is the mean value of an individual‟s progeny, which comes close to the breeding value. The value of an individual is judged by the mean value of its progeny known as breeding value. It is equal to the sum of average effects of genes;, the individual carries.‟ Progeny testing prolongs the generation interval. As the bull had to wait its progeny test result before „its use, but it is more than made up by the increase in accuracy of selection. A higher intensity of selection is also possible by employing Artificial insemination with pedigree semen. Culling of Dairy Animals: Culling is elimination or weeding out of undesirable animals from the herd for reasons of uneconomic, poor production, or very poor reproductive ability, with sterility problems and breeding, irregularities, very poor conditions, stunted growth, suffering from incurable illness, or disease animals found to be positive for serious infectious diseases like Tuberculosis, Johns disease, Brucellosis, lost one or more quarters and teats of the under due to chronic mastitis resulting in marked reduction in milk production. Undesirable breed characters present in young animals. When the herd is a pure bred herd leading to disqualifications family lines, exhibiting heritable characters like supernumerary teats, loose horns in cows of certain breeds. Disable animals due to injury or loss of
  13. 13. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 13 organ, extreme lameness leading to unmaintainable conditions, unhealed fractured animals etc., come under the animal proposed or culling. The culled animals carry lower values and a separate list is made for such called animals and it is known as culling list. When the culling cows for poor production, the entire lactation yield is considered and preferably first two lactations are observed and if the lactional yield is less than what is expected from the breed or herd, the animal is included in the culling list.Very old animals are culled, as their maintainance will be uneconomical. Male animals or other animals surplus in the farm or not useful in the farm and they are culled. Calves born much below the normal birth weight are included in the culling. Yearlings animals male or females, stunted much below their normal body weight, bad confirmation are culled. Valuation and culling is done on the farms every year at least once in year. In some farms culling is done twice a year however doing it once a year is must.
  14. 14. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 14 1.1.2. System of Breeding Breeding is defined as the crossing of the male and the female parents to get the off spring for the characters desired. The main breeding methods are 1) In breeding 2) Out Breeding Inbreeding: Inbreeding is the mating of closely related individuals, whose relationship is more than the average relationship of the population. The example is the individual having one or more common ancestors or relatives. The measures of inbreeding is the coefficient of inbreeding. In breeding may be mild, or close inbreeding and line breeding. Close Inbreeding: In this type is inbreeding mating is made between very closely related individuals such as full brothers are crossed with full sisters, or offspring‟s are crossed with parents. Advantage of Inbreeding: i. Undesirable recessive genes may be discovered and eliminated by further testing in this line. ii. The progeny are more uniform than and breed progeny. It increases homozygosis and decreases genetic variance. iii. Breaking down of population into different inbreed lines.
  15. 15. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 15 Disadvantages: i. The progeny becomes more susceptible to diseases. ii. Breeding problems and reproductive failure usually increases. iii. It is difficult to find out the stereo breeding at which it should be discontinued, in order to avoid the bad effects of the system. iv. It depresses‟ vitality in early life than in later life. v. A small breeder stands a good chance of gain by doing too much in breeding. A rule to follow is never to inbreed more than 12 % and then only in exceptional cases. vi. In breeding appears to have little value in dairy cattle breeding programs, because of its numerous detrimental effects. Line Breeding: It is repeated back crossing to one outstanding ancestor, so that its contribution to the progeny is more. In this type of breeding mating are made to concentrate, the inheritance of desired characters of some favored individuals. i. It brings about the uniformity of the required type. ii. The dangers involves in case in breeding can be reduced. The breeder will select the animal for its pedigree giving due consideration for the individual merit. This may result in very little benefit in new generation, in some case having the benefit.
  16. 16. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 16 Outbreeding: It is the opposite of inbreeding. Mating unrelated animals is known as out breeding. It is divided into six classes as detailed below; 1. Pure breeding 2. Line Crossing (Crossing of inbreed lines) 3. Out Crossing 4. Cross Breeding 5. Grading up 6. Species Hybridization Pure Breeding: It is mating of male and female belonging to the same breed. Pure breeding is a sort of out breeding. The examples of pure breeding are Jersey Cow -x Jersey Bull The outstanding advantage of pure breeding is for production of bulls for breeding purpose only pure breeding is to be followed in almost all the breeds except in case of inter-se-mating. It avoids mating of closely related individuals. Cross Breeding: It is mating of animals of different breeds. Cross breeding is followed for breeding animals for milk production and meat production. Zebu breeds of cows and nondescript cows are crossed with exotic breeds like Holstein Fresian, Brown Swiss and Jersey bulls or their semen, to enhance the milk production potential of the progeny.
  17. 17. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 17 Advantage: 1. The desirable characters of the exotic parent are transmitted to the progeny which the indigenous parent does not have. 2. In India Cross-breeding and cows is done by using the exotic bulls and the progeny inherit the desirable characters of the parent like high milk yield early maturity, higher birth weight of calves, better growth rates, better reproductive efficiency and indigenous parents characters like, heat tolerance, disease ability to resistance 3. In pairs the way to evolve new breeds with desirable characters. 4. Hybrid vigor is made use. Of in the progeny 5. Results are seen more quickly in characters like milk yield in the cross bred progeny. Disadvantages: 1. The breeding merit of cross breed animals may be slightly reduced. 2. Cross breeding requires maintenance of two or more pure breeds in order to product the cross breeds. • Dairy Cattle Production and Management Part
  18. 18. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 18 Chapter 3: Breeding Programs The aim of animal breeding is to genetically improve populations of livestock so that they produce more efficiently under the expected future production circumstances. Genetic improvement is achieved by selecting the best individuals of the current generation and using them as parents of the next generation. To select the best animals one needs to define explicitly what is meant with "best". This means that it is necessary to specify the direction in which we want to change the population. Defining the breeding goal is the first step when designing a breeding program. It is useless to design a breeding program if there is no idea of the desired genetic change. NB. A breeding program is the organized structure that is put into place to genetically improve livestock populations. Successful genetic improvement requires breeding programs to have (at least) the following components:  A system to record data on selection candidates. Without data on selection candidates it is impossible to identify the best individuals.  Methods and tools to estimate the genetic merit (breeding value) of selection candidates. This step is called the "breeding value estimation".  A system to select the animals that become parents of the next generation, and mate them to produce the next generation.  A structure to disseminate the genetic improvement of the breeding program into the production population. In most cases, the breeding population and the production population are (partly) separated. Since the aim is to improve livestock production, genetic improvement created in the breeding population should be disseminated into the production population.
  19. 19. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 19 6.1. The breeding goal The breeding goal, or breeding objective, is the starting point of animal breeding. Broadly speaking, the breeding goal is the direction in which we want to improve the population. The choice of the breeding goal affects the structure of breeding programs. Broiler (chicken for meat) breeding programs for example differ from layer (chicken for egg production) breeding programs because improvement of egg production requires another breeding program than improvement of meat production. The breeding goal has a number of characteristics. 1. The breeding goal is a combination of traits. It specifies the relative importance of each trait. In principle, all traits of importance should be included in the breeding goal. Thus the breeding goal only depends on the importance of a trait, not on its genetic parameters. An important trait of low heritability should be included in the breeding goal, whereas unimportant traits should be left out, irrespective of their heritability. 2. The breeding goal should aim at the future. Animal breeding is a long-term activity. It takes a long time before genetic improvement due to selection is expressed in the production population. 3. From an operational point of view, the breeding goal should ideally summarize all traits in a single criterion. A single criterion to express the quality of selection candidates is convenient because animal breeders can simply rank their selection candidates on this value and select the highest- ranking individuals. A breeding goal expressed as a single value can be obtained by weighting all traits by an (economic) factor, so that the breeding goal is a sum of breeding values weighted by their (economic) value.
  20. 20. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 20 Questions should be raised in developing breeding programs are like:  what market the breeding goal is aimed at;  whether the breeding goal should be based on the competitive position of the breeding company or on an economic model of the production herds  Existence of political or market circumstances such as production quota that affect the breeding goal. In Western countries, breeding goals primarily include economically important traits such as milk yield, meat production and egg production. In addition, breeds are often specialized for a single purpose; dairy breeds are kept for milk production and beef breeds for meat production, layers for egg production, broilers for meat production. In developing countries however, the situation is quite different, because livestock is often kept for auto-consumption and not to produce for a particular market. ==========================Message========================== NB. The breeding goal specifies which traits should to be improved, in which direction and the relative emphasis given to each trait. ============================================================= In animal breeding, there are two common approaches to define breeding goals. The first approach is to express breeding goals as a weighted sum of economic values and breeding values. In this approach, economic weighting factors of traits (economic values) are based on an economic model of the production system. The second approach is to express the breeding goal as a set of desired gains for each trait. The desired genetic gain for each trait is based on marketing and commercial considerations of breeding companies. In many cases, desired gains are based on maximizing the market share of the breeding company in the time frame. Breeding goals based on economic models of the production system:
  21. 21. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 21 When breeding goals are based on an economic model of the production system, the economic value for each trait is determined by modeling the effect of that trait on the profit of a production herd. NB. Breeding goals can be expressed in terms of economic values, which express the increase in profit due to a single unit improvement of a trait, or as desired genetic gains. 6.3. Design and evaluation of breeding programs Design of breeding programs: The structure of breeding programs depends on both the species and the breeding goal. The optimum design of a breeding program will differ between species with large reproductive capacity and species with small reproductive capacity, between breeding programs that aim to improve production or reproduction traits, and low heritable traits versus high heritable traits. The question whether the breeding goal traits have high or low heritability is important. In the case of high heritability, (pure line) selection is an adequate tool to genetically improve the population. When breeding goal traits have low heritability, it will be more difficult to improve them by means of selection, and crossbreeding may be a solution. For traits where selection is the best option, the next question is whether breeding goal traits are favorably correlated. If breeding goal traits show a strong but unfavorable correlation, then it will be difficult to improve them within a single population. In that case, the development of separate sire and dam lines may be a solution. When separate sire and dam lines are the best option, then the final step is to choose or develop separate lines and to optimize selection within those lines. On the other hand, if breeding goal traits are favorably correlated then they can be improved within a single breeding population by means of index selection. The final step is then to optimize the breeding scheme, which involves questions related to the size of the population and the data recording strategy.
  22. 22. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 22 Judging the quality of breeding programs Choosing the best breeding scheme among a number of alternatives requires yardsticks to measure the quality of breeding schemes. Such yardsticks can be developed only when there is a well-defined breeding goal. Given that the breeding goal is clearly defined, there are three criteria that summarize the quality of a breeding program. These are: 1. Selection response for the breeding goal. 2. Maintenance of genetic diversity as measured by the rate of inbreeding. 3. Costs of the breeding program. 1. Selection response for the breeding goal traits is the revenue of a breeding program, whereas loss of genetic diversity and financial costs are the expenses of a breeding program. Selection response, loss of genetic diversity and financial costs are expressed in different units. The problem therefore is to combine them into a single criterion for the quality of a breeding program. A comparison of breeding schemes based on selection response and the rate of inbreeding can be done as follows. To avoid long-term loss of genetic diversity an upper limit can be set to the rate of inbreeding. Next, alternative breeding schemes can be judged by comparing their selection response at the same rate of inbreeding. The scheme with the highest selection response at the same rate of inbreeding (e.g. 1%/generation) is the best scheme.
  23. 23. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 23 Evaluation of breeding programs: Once a breeding program is operational it is essential to routinely evaluate the results. Evaluation may consist of comparing realized genetic improvement and rates of inbreeding with values expected when designing the breeding program. When there are clear differences between expected and realized selection response and inbreeding, then one needs to find the causes of those discrepancies and if possible improve the breeding program. Reasons that breeding programs do not yield the expected genetic improvement are: a) the use of inappropriate models for breeding value estimation, for example when the models do not include systematic environmental effects that are present in the data; b) overestimation of the genetic parameters (e.g. h2 ) resulting in biased EBVs and overprediction of the expected response; c) preferential treatment among selection candidates resulting in selection of individuals that received good treatment" instead of genetically superior individuals, and d) unexpected correlated response in other traits. ==================================Message================== ================ The quality of alternative breeding schemes can be judged by comparing selection response, rate of inbreeding and costs of the alternatives. 2. BREEDS OF LIVESTOCK AND THEIR MAJOR TRAITS General characteristics of Somalia Livestock A. Diversity in livestock types: Ethiopia has a diversified topographic and climatic condition. Within this diversity, various livestock breeds or types have evolved; however, there
  24. 24. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 24 are no detailed studies on the identity of each type and their genetic potentials. Classification of Ethiopian Livestock: I) Cattle: generally classified in to four main groups 1. Humpless: Brachyceros sheko (mitzan, Goda) Bench Zone: Hamitic long horn-Kuri (Kouri) 2. Zebu cattle: Arsi, Borana, Barca, Jijiga small zebu, Harar short horned, Jem Jem black, Bale highland zebu and various small short horned types. 3. Sanga: Abigar, Danakil (Afar, Adal, Raya-Keriyu), Raya-Azebo(Oromo- Azebo) 4. Intermediate sanga-Zebu cattle: Arado, Fogera, Horro and Jiddu. General characteristics of Zebu cattle: Hump: Differ in size depending on breed, age, sex, fatness.Function of hump is not well known in all the breeds. Body: Body is usually narrow with sloping rump. Legs: are usually long to keep the distance between the body and ground more so as to avoid heat of the ground. Heat tolerance: Because of low basal metabolic rate, low growth rate, less yield they generate less of internal heat. They have more capacity to dissipate heat by conduction and evaporation. They have short sleek coat, high surface area to body mass ratio and high number of sweat glands. Tick resistance: They are partially resistant to ticks and they have the ability to repel the flies by movement of their skin. Nutritional requirement: They have low nutritional requirement because of small size, low basal metabolic rate. They are highly efficient in digestion of low level of feeding (low quality feed). When there is shortage of feed and bad living condition smaller animals are superior to larger animals. Productivity: Late maturity, longer inter calving
  25. 25. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 25 period, shorter lactation length, poor yield and failure let down milk with out calf. However milk contains higher percentage of fat and solid-not-fat.
  26. 26. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 26 II) Sheep: Ethiopian sheep types are classified into 3 main groups, based on hair type and tail or rump type. Classification Breed Geographic distribution Hairy thin tailed Bonga, Horro Kefa, Wollega Fat tailed Menz, Arsi Bale, Tukur North-Shewa, Arsi and Bale, Wello Fat rumped Black head Somali, Adal Hararghie, Somali, Afar Sidamo, Bale, Wello, Shewa III) Goats: Using various characteristics such as size, color, horn etc. the following classification is done. Breed Geographic distribution Oromo – Sidamo Southern Shewa and Northern Sidamo Arsi – Bale (Gishe) Highlands of Bale and Harargie Somalli Ogaden, Mudugh, Borana Ogaden and Elkere (Somali) Adal (Afar, Danakil) North rift valley in wello and Afar Bati South west wello, Western Ethiopia Dinka Southern Ethiopia Southern Abyssinian Wello Mule
  27. 27. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 27 IV) Camel: There is no classification work, but they are one humped (Dromedaries) V) Horse: Classified in to two, 1. Oromo Horse, 2. Dongola VI) Donkey: classified into four: Jima donkey, Abyssinian donkey, Ogaden donkey and Sennar donkey VII) Mule: Two groups: Sennar mule and Wello Mule VIII) Chicken: No detailed classification work Livestock in Ethiopia are generally poor for most of the economic traits e.g. Milk, meat, power Production egg etc. Livestock do have multi- purpose use Cattle - Draft power, milk, meat, hide, manure Sheep – Hair, meat, skin and milk in some area Goat – Meat, milk, skin, Horse – Draft power (ploughing and pack) and transport Donkey – Draft power as pack and transport Mule - Draft power as pack and transport Camel – For milk, meat and pack and transport Poultry – Egg and meat
  28. 28. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 28 Ethiopian cattle Group Zebu Sanga Intermediate Example – Breed Related types BORAN Somali Boran, Tana land Boran, Kenya Boran DANAKIL Adal Cattle of Jibuti ARADO Tigre, Wellega, Borica Bileri Origin habitat Borana (province of Ethiopia) Ethiopia (South east) (long horned sanga) Low land and semidesert of Eritrea. Rared by Afar and Danakil tribes. North –east Amhara of Ethiopia. Functional traits Birth wt Weaning wt Mature wt 25 kg.M : 23 kg F 170 kg 318 –680 kg. M. 250- 450 kg F -- -- -- -- 250-375 kg.M 200-300 kg.F ---- ----- ---- Dressing % 54-75% V. high -- --- ------ Milk yield Fat L.L 454-1814 kg 4.1-6.8% 139-303 days 200-300 kg 6.8% 160-225 d. --- --- ----
  29. 29. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 29 The following points of comparison bring out the chief differences between Bos taurus and B. indicus cattle: European (B. Taurus) cattle Zebu (B. indicus) cattle 1. No hump 1. Hump present in thoracic or cervico-thoracic region. 2 . Rounded ears, held at right angle to the head. Long drooping ears, pointed rather than rounded 3. Head short and wide. Long and comparatively narrow head. 4. Skin held tightly to body. Dewlap, umbilical fold and brisket small. Skin very lose, often falling away from body in folds Dewlap, umbilical fold and brisket extensively developed. 5. Skin relatively thick, (7-8mm) Skin relatively thin, average thickness 5-6 mm. 6. Large amount of subcutaneous fat especially in mature animals. Relatively small amounts of subcutaneous fat at all stages. 7. Back line straight or relatively straight. Back line high at shoulders, low behind hump, high over pin bones, sloping down markedly over tailbud 8. Hip bones wide and outstanding Hip bones narrow and angular.
  30. 30. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 30 Certain of the above differences have probably been reduced as a results of artificial selection, particularly animal breeding by man, since the species was domesticated. Thus, items 7, 10, 16 and 19 have probably been modified, to a greater or lesser extent, by man. Certain of the features noted are of little or no significance with respect to productive performance or the adaptation of the species to its environment. However, the majority of the factors listed are of great importance in one or other of these respects. 3. VARIATIONS AND ESTIMATION OF GENETIC PARAMETERS Genetic and Environmental variation The variation is raw material on which a breeder works to produce genetically superior animal. The variation noticed in any matric (quantitative) trait arise from two sources Genetic variation: Variation because of particular combination of genes. The genetic variation noticed among animals is transmitted to next generation and any improvement made is permanent important. The genetic variation is caused by Number of loci involved. Exact number of gene loci involved for any quantitative trait is not known. Even if you take one locus possible type of gametes and genotype of progeny is enormous. The recombination of genes due to crossing over leads to several types of gametes. e.g.(with one locus)
  31. 31. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 31 5.1. Current Situation of Somalia Animal Genetic Resources (AnGR) Somalia Farm Animal Genetic Resources are mostly underutilized biological resources Farm Animal Genetic Resources of Somalia: In Ethiopia, classification of farm AnGRs into breeds is far from complete. Classification studies have been conducted on most of the cattle and goat breeds that exist in the country. However, research is at its rudimentary stage for the other species, particularly chickens. Therefore, the list of breeds presented below should be viewed from this perspective. The most common farm animals of the country can be categorized into mammalian, avian and honeybee species. Cattle, sheep, goats, camels, donkeys, horses and mules are the major farm animals that lie under the mammalian category Populations Types/ subtypes /breeds? 44.32 million Cattle---------------25 types or sub-types 23.62 million Sheep------------------13 types or sub-types 23.32 million Goats-----------------15 types or sub-types 6.06 million equines------------------- (4donkey, 2horse, 2mule) 2.31 million Camels---------------------4 types or sub-types 42 million chickens--------------------------5 types or sub-types
  32. 32. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 32 Cattle breeds Indigenous breeds: major cattle breeds identified so far are Arsi, Begayit, Ogaden, Borena, Goffa, Arado, Nuer, Gurage, Jidu, Karayu/Afar, Harar, Horro, Smada, Fogera, Mursi, Raya-Azebo, Adwa, Jem-Jem, Sheko, Ambo, Jijiga, Bale,Hammer, Medenece and Abergelle. Medenece and Abergelle are recently reported by the Tigray Regional Bureau of Agriculture and Natural Resources Development to exist in that part of the country. Since there has not been any exhaustive identification and characterization work, it is possible that new breeds are to be described yet. Out of 25 indigenous cattle breeds, the Borena, Horro, Fogera, Karayu, Arsi and Nuer are the widely used breeds. Sheep breeds Indigenous sheep breeds: Fourteen Ethiopian sheep populations are traditionally recognized as sheep breeds. Microsatellite DNA-based analysis revealed that some breeds could not be separated at the genetic level, resulting in six genetically distinct breed groups. In Table 5.1 breeds and breed groups are listed.
  33. 33. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 33 Table 5.1. Traditional breeds, breed groups, ecology of Ethiopian/somalia sheep Exotic sheep breeds: Exotic sheep breeds introduced for their wool and mutton production are Awassi, Hampshire, Blue-de-main, Merino, Romney, Corriedale and Dorper. Crossbreeding of the Menz breed with the five exotic breeds, namely: Awassi, Hampshire, Bleu-de-Main, Romney and Dorper are being used for development and research activities. Goat breeds Indigenous goat breeds: Major goat breeds existing in the country are Begayit, Ille, Afar, Hararghe Highland, Arsi-Bale, Short-eared Somali, Woyito-Guji, Long- eared Somali, Central Highland, Abergelle, Western Highland, Widar, Western Lowlands, Maefur and Keffa. Moreover, Felata, Arab, Gumuz, Agew and have been recently reported. Equine breeds Donkey breeds that exist in the country are the Jimma, Abyssinian, Ogaden and Sinnar. Major breeds of horses that have so far been well recognized are the Oromo and Dongola. In Ethiopia, crossing of Asses with mares to produce mules dates back to centuries. Except for two well known, namely: Sinnar and Wollo Mule breeds, there are no other well-defined hybrids in the country.
  34. 34. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 34 In Mekele University,Tigray region, phenotypic characterization of local donkeys has been carried out. However, such activities have to be complemented with proper genetic characterization in order to classify the donkey types found in the region or elsewhere. Camel breeds Attempt to classify Ethiopian camels has not been satisfactory so far. Wilson (1984) has classified and described major camel breeds in the country as the Afar, Borena, Anfi and Somali/Ogaden breeds. Poultry breeds Indigenous chicken breeds: Based on geographical locations, indigenous chicken breeds identified so far are Horro, Jarso, Tililli, Tepi and Cheffe breeds that are found in the central highland areas. The naked-neck breed found in northern, northwestern, western and southern lowland areas of the country. Exotic chicken breeds: Several layer, broiler and dual-purpose exotic chicken breeds introduced into the country are being used for food and agriculture. Rhode Island Red (RIR), White Leghorn, Lawman Brown, Cobb-500, Fayoumi, Bovans Brown, Arob Acre and Bubcocks are reared by small and large-scale commercial producers in urban and peri-urban areas. Besides, RIR and White Leghorns as well as their crosses with indigenous chicken are used by rural smallholders for egg and meat production. Honeybees It is estimated that Ethiopia has about 10 million honeybee colonies. Species of honeybees identified so far are Apis melifera adansol, Apis melifera lementica, Apis melifera monticola, Apis melifera litorea and Apis melifera abyssinica. 5.2.1. PHENOTYPICAL CHARACTERIZATION Phenotypic characterization of AnGR is the process of identifying distinct breed populations and describing their external and production characteristics in a given
  35. 35. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 35 environment and under given management, taking into account the social and economic factors that affect them. The information provided by characterization studies is essential for planning the management of AnGR at local, national, regional and global levels. Characterisation of livestock breeds has been based on description of morphological characters such as horns, ears, coat colour, body size and production and reproductive traits. Since livestock breeds in developing countries have not been subjected to selection for specific traits, considerable phenotypic variation is observed within and among populations with regard to size, horn and ear types and coat colour. Furthermore, most productive traits are polygenetically inherited and are influenced by environment effects, sometimes with a genotype x environment interaction. This leads to some inconsistencies in the classification of the various populations into breeds or strains. Therefore, reliance on phenotypic characters as the basis for characterisation of breeds for sustainable utilization and conservation may be misleading. 5.2.2. MOLECULAR GENETICS CHARACTERISATION DNA marker data provide useful information on the origins, relationships, genetic diversity and gene pool development of domestic animal breeds. The data help to identify those breeds that are genetically distinct. Genetically differentiated breeds can carry genes and gene combinations of economic and scientific importance and which determine an animal's capacity to adapt to particular environments. Molecular genetic characterisation is factual and precise. It is in this sphere that molecular biotechnology has an important role to play. Genetic characterisation of livestock species involves estimation of the genetic uniqueness of the breeds or strains and their evolutionary relationships. This can provide information on which of the populations represent homogenous breeds or strains and which are different. Such knowledge will enable decision-making regarding the choice of breeds or strains for conservation.
  36. 36. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 36 Chapter 5: Breeding Programs The aim of animal breeding is to genetically improve populations of livestock so that they produce more efficiently under the expected future production circumstances. Genetic improvement is achieved by selecting the best individuals of the current generation and using them as parents of the next generation. To select the best animals one needs to define explicitly what is meant with "best". This means that it is necessary to specify the direction in which we want to change the population. Defining the breeding goal is the first step when designing a breeding program. It is useless to design a breeding program if there is no idea of the desired genetic change. NB. A breeding program is the organized structure that is put into place to genetically improve livestock populations. Successful genetic improvement requires breeding programs to have (at least) the following components:  A system to record data on selection candidates. Without data on selection candidates it is impossible to identify the best individuals.  Methods and tools to estimate the genetic merit (breeding value) of selection candidates. This step is called the "breeding value estimation".  A system to select the animals that become parents of the next generation, and mate them to produce the next generation.  A structure to disseminate the genetic improvement of the breeding program into the production population. In most cases, the breeding population and the production population are (partly) separated. Since the aim is to improve livestock production, genetic improvement created in the breeding population should be disseminated into the production population. 6.1. The breeding goal
  37. 37. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 37 The breeding goal, or breeding objective, is the starting point of animal breeding. Broadly speaking, the breeding goal is the direction in which we want to improve the population. The choice of the breeding goal affects the structure of breeding programs. Broiler (chicken for meat) breeding programs for example differ from layer (chicken for egg production) breeding programs because improvement of egg production requires another breeding program than improvement of meat production. The breeding goal has a number of characteristics. 1. The breeding goal is a combination of traits. It specifies the relative importance of each trait. In principle, all traits of importance should be included in the breeding goal. Thus the breeding goal only depends on the importance of a trait, not on its genetic parameters. An important trait of low heritability should be included in the breeding goal, whereas unimportant traits should be left out, irrespective of their heritability. 2. The breeding goal should aim at the future. Animal breeding is a long-term activity. It takes a long time before genetic improvement due to selection is expressed in the production population. 3. From an operational point of view, the breeding goal should ideally summarize all traits in a single criterion. A single criterion to express the quality of selection candidates is convenient because animal breeders can simply rank their selection candidates on this value and select the highest-ranking individuals. A breeding goal expressed as a single value can be obtained by weighting all traits by an (economic) factor, so that the breeding goal is a sum of breeding values weighted by their (economic) value. Questions should be raised in developing breeding programs are like:  what market the breeding goal is aimed at;  whether the breeding goal should be based on the competitive position of the breeding company or on an economic model of the production herds  Existence of political or market circumstances such as production quota that affect the breeding goal.
  38. 38. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 38 In Western countries, breeding goals primarily include economically important traits such as milk yield, meat production and egg production. In addition, breeds are often specialized for a single purpose; dairy breeds are kept for milk production and beef breeds for meat production, layers for egg production, broilers for meat production. In developing countries however, the situation is quite different, because livestock is often kept for auto-consumption and not to produce for a particular market. ========================Message========================== NB. The breeding goal specifies which traits should to be improved, in which direction and the relative emphasis given to each trait. ========================================================== In animal breeding, there are two common approaches to define breeding goals. The first approach is to express breeding goals as a weighted sum of economic values and breeding values. In this approach, economic weighting factors of traits (economic values) are based on an economic model of the production system. The second approach is to express the breeding goal as a set of desired gains for each trait. The desired genetic gain for each trait is based on marketing and commercial considerations of breeding companies. In many cases, desired gains are based on maximizing the market share of the breeding company in the time frame. Breeding goals based on economic models of the production system: When breeding goals are based on an economic model of the production system, the economic value for each trait is determined by modeling the effect of that trait on the profit of a production herd. The breeding goal (H) is expressed as a weighted sum of true breeding values and economic values, NB. Breeding goals can be expressed in terms of economic values, which express the increase in due to a single unit improvement of a trait, or as desired genetic gains. 6.2. Components of breeding programs 1.Data recording and collection: Estimation of breeding values requires phenotypic data on selection candidates. Thus a system has to be set up to
  39. 39. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 39 routinely record data on selection candidates. The way data is collected depends on the species and the traits in the breeding goal. Dairy cattle breeding schemes therefore have a system to record data on daughters of test bulls. Milk yield of those daughters is recorded on common dairy herds, meaning that farmers are involved in the data recording. In beef cattle breeding, growth performance of bulls can be recorded on the selection candidates themselves, meaning that progeny testing is not necessary. In beef cattle breeding, data collection therefore takes place at testing stations where the performance of selection candidates is recorded. 2.Selection and mating: Selection and mating takes place after breeding values are estimated. Selection refers to the process of choosing parents to produce the next generation, whereas mating refers to the pairing of selected individuals. Thus selection precedes mating. The selection process determines the genetic improvement of the population over time, whereas the mating process determines how maternal and paternally derived alleles are combined within individuals. 3. Dissemination of genetic progress: In most species, the breeding and production population are distinct. Genetic progress is created in the breeding population, but the final aim is to improve livestock production in the entire population. Thus genetic improvement created in the breeding population has to be disseminated into the production population. In dairy cattle, the breeding and production populations are not strictly separated. Superior cows from the production population can enter the breeding population, meaning that they are selected as bull dams. Genetic progress created in the breeding program is transferred to the dairy farms by the sale of semen of progeny tested bulls to the farmers. The sale of semen is the primary source of income for dairy cattle breeding companies. =======================Message======================== A breeding program has the following components: i) a data recording system, ii) methods and tools for breeding value estimation, iii) a selection and mating 4. INBREEDING AND RELATIONSHIP
  40. 40. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 40 All the living beings are interrelated. The relationship between any two individuals is due to procession of some common genes they have because of immediate or remote ancestor in their decadency or lineage or heritance. It is the brood sense of relationship. But for practical purpose any two individuals are said to be related if they have one or more ancestors in common at least in first six generations. After six generation because of halving of remote ancestor‟s hereditary materials two individuals would have little genetic relationship. The relationship is categorized into three groups (a) Direct relationship (b) Indirect or collateral relationship (c) Combination of direct and indirect relationship Direct relationship: If occurs between individual and its ancestor or between individual and descendant. It arises when out of two individuals one is direct ancestor (parent) other is descendant (progeny). The relationship between the parent and offspring is 50 percent or 0.50 because one half of the offspring‟s genes are obtained from one of the parent i.e. 50% of parental and offspring‟s genes are same. The parent offspring relationship is the simplest one. Indirect or collateral relationship: This kind of relationship exists when relatives are not directly related to each other or descendant in lineage because they are not ancestors or descendants of one another. However they have one or more ancestors in common. e.g. Full sibs, half sibs, cousions etc where in both the individuals, receive common genes from their ancestors.. Combination of direct and collateral relation ship This type of relationship is seen when an outstanding individual is mated to is descendant and also to its collateral relatives. If the ancestor appears in
  41. 41. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 41 pedigree more than once relationship between the individual and ancestor in question is always greater than if ancestor had come only once in lineage or pedigree of an individual Measurement of inbreeding Inbreeding (mating of related animals) has many effects on genotype and phenotype. Inbreeding increases the homozygocity and it decreases the heterozygocity. All the good and bad phenotypic effects are because of this increased homozygocity or loss of heteroyzyocity. Therefore it is important to measure amount of inbreeding of an individual or herd. The term inbreeding coefficient (F) is used for this purpose which measures the increased homozygocity. Homozygocity, a likeness of two genes may by state (chance). They are two randomly drawn genes from population and by chance they are alike. It is known as identical by state. Two genes of an individual may be alike by descent. It is because of mating of relatives. Alikness arise from replication of same genes from common ancestor. It is known as identical by descent. Thus inbreeding coefficient is probability that two alleles at a locus in an individual are identical by descent. It is measure of decrease in proportion of heterozygous genes over what was present before inbreeding is practiced. It is always a measure relative to some starting point, some generation back for which F is considered as zero, It two individuals have no common ancestor in past six generation. 5. METHODS OF GENETIC IMPROVEMENT Selection In random mating in large population, in absence of selection, mutation, migration the gene frequency remains constant. Hence we assume that each individual of the population contribute equal number of gametes to the population. Each individual will contribute to next generation in proportion
  42. 42. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 42 of frequency of genotype in current generation. Since there is no change of gene frequency no change of phenotypic properties is expected. But the nature or men do not allow each individuals to contribute equally to the gamete pool. Nature allows most successful genotype to multiple and men allow most useful genotype to multiply. Therefore certain individuals are preferred to others in production of next generation. Thus selection is choosing of parents of next generation either by nature or by men. It is designation of parents of next generation. The process of differential reproduction among the individuals of different genotype is known as selection. Selection Natural selection Men made selection (Artificial selection) The natural selection depends up on the genetic differences among the individuals in fitness characters such as disease resistance. Libido, mating behaviors, anatomical and physiological superiority. It is the survival of the fittest. Only strong and these adapted to environment survive and produce large number of offspring‟s. In artificial selection breeder determines which animal to reproduce, which will be retained for replacement, how long they will be allowed to remain in population. Both natural and artificial selection do occur simultaneously in a population. They may influence the same or different traits same or in opposite direction. Selection is practiced by nature or men at any stage of
  43. 43. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 43 life. Some are not allowed to born some are born and die before they reproduce, some are culled because of their bad pedigree, some are culled after their own performance and some are culled after knowing their progeny performance. Objective of selection 1. To improve the overall productivity which includes utility, survivability etc Principles of selection 1. Variation is basis of selection. 2. Selection is effective when the traits selected are heterozygous. 3. When a race / breed / herd becomes homozygous for certain trait selection no longer improve it. 4. Selection should be based on hereditary variation and not on environmental variation. 5. Selection does not create any new genes. 6. Selection increases the frequency of desirable genes. Selection will be effective and meaning full if systematic recording is practiced. But even without the knowledge of Genetics selection was highly effective. The difference between the performance of breeds of present day and primitive type of animals is the best of example of effect of selection. Type of selection Directional selection: The breeder select the individuals to be the parents of next generation whose phenotype are more nearly approach a maximum (milk yield) or minimum (back fat thickness in pigs) for some trait. Other individuals with poorer phenotype are not allowed reproduce. If the trait is heritable than the part of phenotypic superiority of selected parents will be
  44. 44. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 44 passed on to the next generation. Next generation will be above the population average. The favorable genes frequency will be increased. Therefore the effect of directional selection based on phenotype variation is due to genotype. It will increase the gene frequency of favorable genes and decrease the gene frequency of undesirable genes. Directional selection is practiced utilizing the records of ancestors, individual, progeny, collateral relatives. Factors affecting the selection progress Many physical, biological and management factors affect the selection progress. 1. Ability of the breeder: Progress of selection depends upon the ability breeder to select the superior breeding stock. He should have a definite goal (objective) in his mind and should not change it often. He should have accurate records for comparison. The popular type of this year may not have the same favor in coming years. So the selection progress can be slowed down. Hence should have a plan well in advance for the future trends and need of the people 2. Foundation stock: Selection will be ineffective if the foundation stock is poor. If the genes which are desirable are not found in the foundation stock or are very rare then the selection will be powerless. In that case the desirable genes have to be introduced from outside (out breeding) 3. Level of performance: If the population performance is uniform the difference between the selected and rest will be less. Similarly the selection becomes ineffective if the herd average for that trait is very high. Then it will be difficult to find animals that exceeds the herd average. This occurs
  45. 45. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 45 due to long time selection and decrease in genetic variability. By outbreeding (introducing new genes) and changing the environment variation can once again brought about for further selection. 4. Number of traits considered for selection: Simultaneous selection for large number of traits reduce the selection intensity for any one trait. Only those traits which are economically important should be considered. Less important traits such as color, shape of the ear, shape of horn etc which have no influence on the performance should not be taken for consideration during the selection. 5. Heritability of the trait: The qualitative traits are more heritable than the quantitative traits. If the heritability of coat colour is one (100%) this character is completely inherited from parent to offspring. If the h2 of the trait is high selection progress will also be high because a large portion of selection difference is due to heredity and not due to environment. Any difference in environment can not be transmitted to next generation. 6. Selection differential: Larger the selection differential more will be the selection progress. 7. Length of time selection is practiced: Improvement of performance traits in large animals is slow and takes long period of selection. Further progress in single generation is likely to be masked by environmental effect. It takes few generation to note the real progress. 8. Generation interval: By reducing the generation interval one can increase the selection progress. 9. Genetic correlation among the traits selected: While selecting for two traits at time if improvement in one traits brings about the improvement in another also the total progress will be more. e.g. Rate of gain and efficiency of gain. If the two traits are negatively correlated than the total progress will be less or nil.
  46. 46. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 46 e.g. Milk production and draft capacity. Concept of Breeding value and transmitting ability Suppose in beef cattle herd selection is based on the yearling weight Herd average 200 kg Selected bulls yearling wt 250 kg Selection differential 250 – 200 = 50 kg Heretability of yearling wt 0.50 Genetic gain 50 x 0.50 = 25 kg Average of the progeny of 200 +25 this bull = 225 Aids to selection There are several sources of information available to increase the selection accuracy or probable breeding value of the individual. Some information is from individuals own performance some are from their relatives Individual selection (mass selection) Selection is based on the performance of individual itself. The phenotype of individual is the sole criterion for estimating his genotype (Genetic merit). This is also most commonly used basis for selection in livestock. It is effective when the heritability of the trait is high, indicating that the trait is greatly affected by additive gene action. High h2 estimate also suggest that phenotype strongly reflects (correlated with) genotype. Further the
  47. 47. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 47 individuals that are superior for particular trait should also poses desirable genes for that trait and should transmit these genes to their offsprings. But one should provide standard environment to distinguish between the genetic and environmental effects. Advantages: .1.Simple since the characteristics such as milk yield, growth rate, fleece wt etc can be directly evaluated from the individual itself. 2. Selection can be made even without the knowledge of the pedigree. 3. Less time consuming compared to progeny testing. 4. All the animals can be evaluated, whereas in progeny testing only limited number of animals can be evaluated. 5. Can be used as preliminary selection before progeny testing. Disadvantages 1 Many of the economically important traits are sex limited and hence expressed only in one these sex. (Female). Therefore selection of males cannot be based on their own performance for the traits (milk yield egg yield)
  48. 48. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 48 2 .Records of milk yield, egg yield etc are available only after the sexual maturity. Therefore selection has to be postponed till such time. 3. Slaughter traits such as carcass quality, dressing percentage etc can be assessed only after Slaughter of the animal. Therefore it is of no help in selecting for these traits. 4. In case of traits which have low h2 individual merit is a poor indicator of the genotype. Therefore the improvement from individual selection will be less for such traits. If the superiority of performance of an individual is due to heterozygosity it will not be transmitted to the offspring. Methods of selection 1. Tandem method: Selection is practiced for only one trait at a time until satisfactory improvement is done in this trait. Then the second trait is considered for the selection and so on. If there is a positive correlation between the first trait selected and any other trait both will improve. If there is negative correlation, progress in one trait is affected by a decrease in other and will nullify the effect e. g milk yield and fat percentage, Heat tolerance and milk yield. Disadvantages. Least efficient method More effort and time consuming Negative correlation between several economic traits will nullify the improvement
  49. 49. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 49 2. Independent culling method Selection is practical for two or more trait at a time. For each trait a minimum standard is set. Animal should meet standard for selection. Failure to meet the set standard for any one trait will disqualify the animal. e. g Character Birth wt AFC Milk yield fat % Min. standard 30 kg 30 m 2000 kg 5 % This has been usually used in past for type and confirmation traits (color, size, horn) in show cattle regard less of economic value Advantage 1. Selection for more than two traits at a time will bring about simultaneous improvement. 2. Animal can be culled at an early age for failure to meet the minimum standard thus reduce The cost maintenance. Disadvantages 1. An animal is culled for failure to meet the minimum standard set for one trait although it is superior in other traits. (4.5 % fat 3000 kg milk). 2. Animal may culled at an early age for its failure to meet the minimum standard without giving chance to reveal superiority in later stage of its life. (i e a female calf weighing 24 kg will be discarded. Without giving chance for future i.e production. Selection index method (Total score card method) In this method value (marks or score) is separately determined for each of the trait selected for and these values of each trait selected is added to give
  50. 50. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 50 a total score for all the traits. The animals with higher total score are selected. The value for each of the traits defendants upon a) Relative economic value of the trait All the traits selected are not equally important and carry equal marks b) Heritability of the traits. Higher the h2 more the value c) Genetic correlation with other important trait Advantages 1. One of the advantage of this method is even though animal is slightly deficient in one trait and if it superior in other trait it will be saved. 2. The efficiency of this index selection is more than that of independent culling level and efficiency decreases as more traits are involved. If the „n‟ is number of traits then an index is n times as efficient as independent culling level Disadvantages 1. Construction of selection index under is highly complex 2. The genetic parameters (heritability, correlation) and economic values are not constant for all the populations and in all the time and depends on many factors thus lead to revise the index. Selection based on progeny performance (progeny testing) It is the estimation of breeding value or genetic worth of an individual from the study of the performance of its offsprings. It is being increasingly used as an aid in estimating the genetic worth of an individual. The idea of progeny testing is not new. About 2000 years ago it was advocated by
  51. 51. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 51 Varro of Rome. Robert Bakewell used the outstanding sires after knowing the performance of their progeny in 18th century. the dams. Principle: The principle underling the progeny testing comes from the sampling nature of the inheritance where each offspring receives a sample half of the gene from its parent. Each additional offspring receive another independent sample from same source. Selection based on collateral relatives: Collateral relatives are those individuals who are not directly related either as ancestor or progeny. e. g full sibs, half sibs They do not contribute any gene to their relatives. But they have certain common genes which they have received from their common ancestors. Thus average performance of collateral relatives gives an indication of genetic makeup of an individual. More closely collateral relatives are related to the individual more accurate is the estimation of its genetic worth. Therefore selection based on the information of full sibs is more accurate than that of half sibs. Advantages of selection based on collateral relatives: A. For sex limited traits Selection of bulls based on milk production of his half sibs, full sibs. B. For slaughter traits (carcass traits) Slaughtering the half sibs / full sibs to evaluate the carcass quality c. Less time consuming compared to progeny testing d.Less generation interval compared to progeny testing
  52. 52. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 52 e. Useful for traits of low h2 Though less accurate than progeny testing the generation interval is less in selection based on collateral relatives. Therefore it may be almost equal to progeny testing in genetic improvement obtained. Family Selection In livestock selection, family can be classified into three types. 1. Sire family; These are the offspring of one sire out of different dams, may be born in same year or born over number of years. 2. Dams family: These are the offspring‟s of one dam out of different sires may be born in same year or in different years. In case of cattle and sheep superovulation of dam and Invitro fertilization by sperms of different sires. Can give this type of family. 3. Sire and dam family These are the offspring‟s by one sire and one dam. These offspring can be obtained by in same year or in different years. Therefore family is usually made up of full sibs or half sibs. The families of remote relationship being of little practical importance. Full sibs‟ family selection is practiced when reproduction rate is high (pigs, poultry) and half sib family selection when reproductive rate is low (cattle, sheep). However in poultry the sire family selection is more efficient than the dam family selection when h2 is near about zero and less than 0.10. Since h2 of egg production is approximately 0.10, sire family selection is usually practiced for improving the egg production.
  53. 53. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 53 Mating systems The mating systems govern the breeding plans that are aimed to harness the favorable gene combinations to maximise the net profit to the farmers. Generally mating systems are executed immediately ofter successful selection of suitable parental genotype to produce progeny of the next generations. Therefore mating system is one of the ways open to the breeder for a) Changing the genetic constitution of progeny generation over population. b) Improvement of the performance of progeny generation over base population. General objectives of mating systems  To produce the future progeny of good genotype to make further profit.  To bring together the desirable gene combination after selection  To bring the genetic uniformity  To enhance the relationship  To Ancash the effect of heterozygosity  To overcome the hereditary defects  To form a base for synthesis of strain / line / breed. Effects of mating systems:  Alter the gene frequency (Hardy Weinberg equilibrium is altered.)  Cause genetic uniformity / purity / and therefore increase the pre potency  Cause the heterozygosity (heterosis)
  54. 54. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 54 Broad classification of mating system Based on genetic relation ship Random mating Nonrandom mating Inbreeding Out breeding Random mating: It is system of mating in which individual of one sex is equally likely to mate any other individual of opposite sex in a given population. It is also called as “Panmixie” Nonrandom mating: It is also known as “Selective mating” in which case, the selected male is mated with selected female. Out breeding: It mating of genetically less closely related individuals than average of the population. It is known as out breeding. Inbreeding Mating of closely related individuals compared to average of the population is known as inbreeding. Inbred individual carry more of identical genes by descent.
  55. 55. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 55 Objective  To increase the relationship to an outstanding sire or dam.  To increase Homozygocity Genetic purity Uniformity  To eliminate the recessive undesired alleles  To form distinct lines/strains/family or seed stock from highly heterozygous population  To increase the prepotency (ability to produce its on type) due to increased homozygocity. Disadvantages  Too many progeny have to be  slow increase of homozygocity Discarded because homozygocity of recessive genes.  Progeny become susceptible  to disease, reproductive problem,
  56. 56. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 56 Chapter 7: Selection and Genetic Change The previous chapters have introduced basic animal breeding theory and have shown how one can estimate the genetic merit (breeding value) of individuals. This and the following chapter will show us how that information can be used to genetically improve livestock populations and how one can quantify the expected genetic improvement. The animal breeder has two tools to genetically improve his populations: selection and mating. 7.1. Selection In animal breeding, the aim is to genetically improve livestock populations by exploiting genetic differences among individuals. Genetic improvement is achieved by selecting individuals that are genetically superior to the rest of the population. The term "selection" refers to the process of choosing parents to produce the next generation. The challenge for the animal breeder is to select genetically superior parents to produce the next generation of offspring, so that only the alleles of those individuals will be passed on to the next generation. Similarly, to prevent alleles from genetically inferior individuals from being passed on to future generations, they should be avoided as parents. In addition, one may decide to produce many offspring of the very best individuals and fewer offspring of sub-optimal individuals. In that case, the very best individuals will contribute more alleles to the next generation than the sub-top individuals. Thus the process of selection determines which alleles are passed on to future generations and therefore determines the genetic composition of the population in the future. It is important not to confuse selection with mating. Selection refers to the choice of parents, whereas mating refers to the "making of pairs" among the parents that are already selected. Thus selection precedes mating. Selection does not create new genes, but increases the proportion of favourable genes in the population. The gains are accumulated when we continue to select the best animals in each generation. A continuous, long-lasting genetic improvement in traits included in the breeding goal is thus achieved.
  57. 57. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 57 There are two kinds of selection, natural selection and artificial selection. Natural selection is the process of survival and reproduction in natural populations. In populations in the wild, the individuals that fit best to the environmental conditions produce the most offspring. As a consequence, those individuals contribute the most alleles to the next generation. Natural selection therefore favours a combination of viability and reproductive ability, i.e. fitness traits. The selection done under human control to obtain genetic improvement of traits in domestic animals is called artificial selection. Fitness traits, such as fertility and disease resistance are usually included in this selection, but large emphasis is given also to many other traits, such as production traits, productivity, product quality, performance traits and longevity. Selections of the cows with the highest milk production or of the fastest growing chickens are typical examples of artificial selection. Selection can be performed both between and within populations (e.g. breeds). To screen animal populations and thereafter use those that have characteristics in line with a desired breeding goal can be a way to get results quickly, assuming the populations can be compared properly. For continuous and long-lasting effects, however, it is necessary to conduct selection within populations. This is what is normally meant by selection for genetic improvement.
  58. 58. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 58 Figure 7. 1. Illustration of how selection effects are accumulated and maintained. From the above figure we can see that:  Using selected animals from the base population as parents results in an increased genetic level of the animals in the next generation (see the column for generation 1).  The selection effect obtained through selection in generation 0 is maintained also in later generations (see the row for selection effects from generation 0).  Selecting superior parents also in subsequent generations further raises the genetic level of each generation.  The selection effects from each generation are accumulated. Thus, the genetic level of animals in generation 5 is built up by selection effects from all previous generations (see the column for generation 5).  The genetic trend per generation is illustrated through the line. The driving force for genetic improvement is of course the genetic superiority achieved by the selection of parents, but also other factors, such as generation intervals and differentiated use of selected breeding animals, have an impact. One should also remember that additive genetic variation is a prerequisite for any selection effort to be successful. The animals in the population must be genetically different with regard to a specific trait. Otherwise it will not be possible to select individuals that are better than others! 7.1.1. Selection strategies The traits we want to improve in a population are defined in the breeding goal. A few of the goal traits might be influenced by simply one or a few alleles, which means that the true genotype often can be determined (e.g. through a DNA test) and it is then easy to select the desired genotypes. The majority of goal traits, however, are quantitative in nature, i.e. influenced both by genes at many loci and by environment. These traits are often normally distributed. Selection is then commonly based on predicted breeding values, which in turn are based on
  59. 59. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 59 phenotypic values and knowledge of heritability, genetic correlations, genetic relationships, economic weights, etc. Selection Directional selection is the most common type of selection. It means that an extreme fraction of the individuals are selected. If a high value for a trait is desirable, then we select the animals with the highest values, e.g. those with high growth rate, milk yield or performance score. If a low value is desirable, then we select animals in the opposite fraction of the normal distribution, i.e. the animals having low values, e.g. for back-fat thickness, disease incidence or time to run a race. Stabilizing selection means that we select a middle fraction of the animals and avoid selecting the extremes. In this type of selection it is the optimum values that are desirable. Examples could be birth weight and quality traits, such as meat tenderness. It is possible also that in species with large variation in litter size one wants to avoid selecting animals giving very small or very big litters. Selection within a population is usually applied in several stages; this is sometimes called stepwise selection.  The first selection event might be based entirely on pedigree information (usually the average of the parents‟ breeding values).  The next events might occur when information is available on animals themselves, and maybe also on sibs; one selection round on traits expressed fairly early in the animals‟ lives, e.g. growth rate,  Another round on traits expressed later, e.g. fertility or performance.  A fourth selection round might occur when in addition to previous information there are also progeny results at hand. There might also be one step for selection of elite animals as parents to the next generation of males to be used in artificial insemination. The best animals in each round of selection are retained to the next selection event, while the ones that are not selected might be culled, or they might be used as production animals, or even as parents to non-elite breeding animals.
  60. 60. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 60 Measuring and keeping records of important traits, and also predicting breeding values without bias and with a high precision, is fundamental for a functioning selection program. The accuracy by which we are able to rank the individuals determines the success of a selection among them. 7.1.2. Selection schemes Various schemes are adopted for the selection of the best animals into breeding herd. In the simplest methods, animals can be selected on the basis of: a) their own performance records (individual selection or mass selection), b) progeny records (progeny testing) c) their family mean (family selection) or pedigree selection). Literally all of these methods of selection use the available information about each animal‟s breeding value in order to determine the genetic worth of the animals through development of an index of merit. a) Performance Testing Performance testing is basically selection of genetically superior animals on the basis of their own records of economically important performance traits. In this method, animals are tested either on-station or on-farm. In each case, performance data for the traits under consideration are recorded and analysed to estimate the breeding values for the animals. If selection is based solely on the basis of the animal‟s phenotypic values, it is also referred to as individual selection. There are some conditions that must be met for maximum response to be attained from this scheme: -  The production traits must be accurately measured and correct records of performance maintained. Inaccurate measurements, just like inaccurate records, result in misleading predicted breeding values resulting in poor performing animals being selected for breeding. This will impact negatively on overall productivity and performance of the farm when the cost of maintaining a wrongly selected animal  The breeder must ensure that the animals being considered for selection are from the same contemporary groups that had equal provisions in terms of age, sex, management including feeding, treatment, vaccinations
  61. 61. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 61  All predictable fixed effects (environmental factors) should be pre-adjusted for before genetic evaluation of the animals is carried out. If all the above conditions are met, performance testing provides the simplest selection scheme and apparently gives the most rapid response to selection However, this scheme has its own Disadvantages: -  Some traits are sex-limited being expressed only in one sex. As such, performance testing cannot be conducted in both sexes and this has a tendency to limit the progress of genetic improvement  Some traits can only be measured very late in life when the animal is approaching the end of its economic value. In beef cattle breeding, some traits like carcass quality are measured after slaughter and thus such records cannot be utilized in performance testing  This scheme is of little significance for traits of low heritability, because of the very low genetic progress realized from selection on its basis. b) Progeny Testing This is a form of family selection that is widely used in animal breeding. This method is based on the principle that the mean performance of a progeny group should give a reliable indication of the estimate of the breeding value (EBV) of one or other of its parents, since each offspring receives a random sample of genes from both parents (half of them from each parent). As such the selection criterion with this system is the mean value of an individual‟s progeny. Progeny testing estimates the breeding value of one parent, on the basis of performance of its progeny. Dams are not usually progeny-tested because of the limited number of offspring that they produce in their lifetime. Procedure for progeny testing  Potential parents are mated to a random sample of dams within a herd;  The resultant offspring (progeny) are measured for performance on the traits under consideration;
  62. 62. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 62  On the basis of the progeny group average, and after weighting for the different number of progeny per parent, the breeding parents are selected from the group potential parents.  Selected parents are mated to produce a second batch of progeny which become the next group of parent to be progeny tested. Limitations of progeny testing  There is a lengthened generation interval since the selection of the parents cannot be carried out until the progeny have been measured.  There is possibility of generations overlapping and this further complicates the evaluation of the parents.  There is a possibility of ambiguity since the progeny will be tested just when the parents are being tested. There is a real possibility of using both as parents. c) Pedigree selection The pedigree of an animal is a record of all the ancestors, recent and remote that are related to the animal under consideration. In this respect, knowledge of the genealogy of the animal alone may be of limited use in pedigree selection but rather, the productivity of all these ancestors to the individual animal. Pedigree selection therefore estimates the breeding value of an animal on the basis of production performance of its ancestors. If the performance of an individual animal is known with precision, it may not be wise to carry out pedigree selection but rather individual selection. Pedigree selection is only useful when: -  Progeny performance data are not available;  The animals to be selected are so young such that their individual merit cannot be ascertained with any degree of certainty;  Selection is being made for animals with comparable individual merit. Pedigree selection has several advantages including that it is: -  Relatively less expensive to carry out since it uses only records.  Useful for initial selection of those traits that are expressed in one sex only.  Selection can be carried out early in the life of the animal to be selected. The disadvantages of pedigree selection include: -  It puts undue emphasis on relatives, particularly remote relatives, resulting in a reduction in the intensity of individual selection.
  63. 63. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 63  It is biased towards progeny of favoured parents having been selected previously 7.1.3. Multiple trait selection methods The goal of multi-trait selection is to increase the net merit of the population. Thus, one important factor in designing multi-trait selection schemes is the relative economic value of a unit genetic gain in each trait included in the selection program. The most effective way to account for differences in the economic worth of each trait is to weight each trait by its economic value so that each component breeding value in the aggregate breeding value is improved in proportion to the economic gain expected. There are three recognized approaches to multi-trait selection, although many operational selection programs combine parts of more than one method to achieve various breeding goals. The three selection methods are: a) the tandem selection procedure b) independent culling method c) the index selection procedure, a) TandemSelection This method of selection involves selection for each trait singly, but is sequence. Selection is first carried out for the most important trait, based on economic value of genetic gain and predicted genetic gain, for a given number of generations. Once the goals for the first trait have been achieved, selection effort is targeted to the next most important trait, and carried out for specified number of generations. The process can continue indefinitely, for any number of traits. Often in practice, the tandem method is superimposed on top of the other two methods of selection to provide long-term flexibility in changing traits targeted for selection
  64. 64. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 64 as market conditions change. As is true for all three methods of selection, tandem selection has advantages and disadvantages. Advantages of Tandem Selection: It is the simplest of the three methods and requires the least amount of detailed information. Prediction of selection response is simple since response for each trait in sequence can be predicted using the simple equation for truncation selection on a single trait. In addition, the method can take advantage of favorable genetic correlations with other traits, allowing correlated genetic gain in secondary traits to offset the cost of selection. Frequently, the tandem method is applied when a population is first placed under domestication or a new breed is under initial development. Under such conditions, little genetic information is available for traits because of the newness of the population so the simplest approach is to choose a single trait with high economic value to initiate the program. As more information is acquired regarding additive genetic variances and phenotypic and genetic correlations, the program can be modified to address other important traits. Disadvantages of Tandem Selection: It is difficult to set a goal representing the desired end point for selection on each trait in the sequence. Tandem selection can have a major negative impact on net merit of the population if unfavorable genetic correlations exist between the trait under selection and any other trait important to net merit. b) Independent culling level This method is used in multiple trait selection. The implementation of this method based on setting a minimum level of performance for each trait included in the selection program. The selection procedure is simple truncation selection for each
  65. 65. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 65 of the traits based on the culling level specified for each trait. The culling levels are said to be independent because once the culling levels are established for each trait selection proceeds on each trait without reference to the performance of individual animal may exhibit for other traits. Culling is a procedure used to remove under- performing animals from a production herd so culling decisions is based on some estimate of producing ability. Example: Consider a program for the selection of heifer replacements for a beef cattle population, designed to increase yearling weight but to keep birth weight below at maximum accepted level. Selection for yearling weight may be desirable because increased weight would reflect rapid growth rate and would increase the number of heifers that could be bred for the first time at one year of age without impairing their long-term reproductive performance. On the other hand, controlling or reducing birth weight would reduce parturition problems in the herd. Advantages of independent culling method  relatively easy to apply because the procedural rules are very direct; determine the culling levels and select all individuals meeting or exceeding the culling levels.  The method can be very effective for qualitative characters such as coat color, general body conformation or physical soundness.  The method is also convenient when selection can be carried out in steps over the life time of the animal.  This approach allows flexibility in determining the importance of the various traits to net merit by adjusting the selected proportions to achieve the desired final result (based on economic values and predicted selection response). Disadvantages of independent culling method There only two difficulties in applying the independent culling levels method of selection.  It is difficult to establish culling levels that truly reflect the economic value and expected selection response.
  66. 66. Printed by: Daacadprinting center, 0633500000 Lecturer: Abdirahman Awsamire (MSc.) Faculty of Animal Science 66  Preventing arbitrary modifications to the culling levels, because of short-term changes in market conditions or the attitude of the breeder.

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