Animal Evaluation and Selection - Growth Curves

1. Ch. 2: Growth, Development, and Fattening of Meat Animals
Live Animal Selection &
Carcass Evaluation

2. Course Announcements
• Quiz #1
• in class Thursday, March 9th
• 8 wks, this semester will go fast!
• Ch. 1 & Ch. 2 Assignments
• due Thursday, March 9th, on Canvas at 2:29 pm (before class)
• Friday Canvas Activity
• opens Thursday at midnight and is due Monday, March 20th at 2:59 pm
(don’t forget during Spring Break)

3. Growth & Development
• Development – not all portions of the body develop equally or at the same
time during growth, growth difference from embryonic stage to maturity
• the head of all animals comprises a larger portion of the body at birth than at any
later stage of its life
• the head’s post-natal development increase is less than other body parts
• the legs of calves, lambs, and foals comprise a larger potion of the body at birth than
at later stages – develop less than other body parts during postnatal growth
• the legs of pigs require considerably more development during postnatal growth in contrast
• Growth – an increase in the structural tissues; an increase in the bone,
muscle, and connective tissues associated with muscle
• does not include fat tissues

4. Importance of Growth & Development
• Importance of Muscle – MEAT consumption
• Importance of Skeletal Structure and Soundness – maximizes
production efficiency during the growth of the animal and to ensure
longevity of breeding stock
• Importance of Fat – acceptable eating quality, palatability and
protection during storage and handling prior to fabrication

5. Normal Growth Curve
• sigmoidal/S-shaped curve
• the growth of an animal is typically step-like and generally
follows this curve for growth and development
• Bone
• Muscle
• Fat
• Growth Units: grams, kilograms, or pounds
• Time Units: days, weeks, months, or years
• relatively little growth occurs prior to birth, and the increase in growth units following birth is
initially very slow
• followed by a rather rapid increase in growth units relative to time (the steep part of the graph)
• Stage for most efficient gains, rapid growth in short amount of time
• growth rates tend to then level off as the animal approaches mature size (upper part of the graph)
• all tissues have ceased or are slowing their rate of growth and development

6. Growth & Development of Bone, Muscle, and Fat:
• Fat & Muscle – sigmoidal shape
• Bone – relatively straight line
• due to the early maturity of bone, bone is typically matured at or about weaning age with a
relatively little further increase during the period of maximum growth of muscle and fat
• The arrow represents the approximate
point of the Choice quality grade of beef,
carcass should have 30% fat at this point
• Efficient production of meat animals with
maximum muscle and minimum fat is the major
goal of the livestock industry
• Consumer attitude & demand, fat is generally
considered undesirable
• Bone is waste
• A certain degree of fat is necessary for protection against dehydration and discoloration, and storage

7. Marbling
• Fat within muscle tissues
• Used for quality grading in cattle and sheep
• Adds tenderness, juiciness, and palatable flavor

8. Fat Deposits
1. Under the skin – Subcutaneous Fat
2. Between muscles – Intermuscular Fat
3. Within muscles – Intramuscular Fat
4. Around the kidney – Kidney Fat

9. Subcutaneous Fat
• Subcutaneous Fat – fat measured on the back of livestock species or
their carcasses, “backfat”
• Easily measured and estimated
• Sheep - called belly wall thickness
• Swine – measured at shoulder, 1st rib, and 10th rib
• Makes up 70% of swine carcass fat
• Cattle – measured at rib, loin, brisket, and cod
• Makes up 40% of the fat on a beef carcass

10. Intermuscular Fat
• Intermuscular Fat – fat between the muscles, “seam fat”
• not easily estimated
• not included in live animal or carcass evaluation procedures we will conduct
• important in pricing of primal, sub primal, and retail meat cuts
• Makes up 42% of fat on beef carcass
• Makes up 15% of pork carcass fat
• Muscle Boning - separation of muscle from fat

11. Intramuscular Fat
• Intramuscular Fat – fat with the muscles, “marbling”
• Important in beef carcass evaluation and grading
• Used in evaluated ribbed lamb and pork carcasses, but not in grading these
carcasses
• Flank Streaking - fat in the flank muscles of sheep, used to quality
grade lambs
• Feathering - evaluated in rib muscles of swine carcasses
• Makes up 15% of fat on beef carcass
• Makes up 9-10% of fat on sheep and swine carcasses

12. Kidney Fat
• Kidney Fat - deposit of fat in abdominal cavity around kidney, pelvis,
heart, “KPH Fat”
• 1st deposit of fat to develop
• If marbling is high, KPH Fat content will be high
• KPH Fat is waste fat, removed at slaughter
• makes up 13% of beef and lamb carcass fat
• makes up 5% of swine carcass fat

13. Carcass Fat Distribution
Subcutaneous
Fat
Intermuscular
Fat
Intramuscular
Fat
Kidney
Fat

14. Physiological Age
• Physiological Age – difference in stage of maturity among animals of
the same species and chronological age
• Occurs during the onset of puberty
• Refers to the maximum body weight and height of the animal
• Difference body compositions, breeds, species, sex classifications, and individuals have
different physiological ages

15. Physiological Age cont.
Physiological Age
Physiological Age effects the skeleton, vertebrae,
ribs, and color of lean muscle tissue
Effects skeleton
makeup, ossification,
and calcification
Effects carcass merit
results and carcass
quality, fat deposit,
and age
Effects secondary sex
characteristics of males
and females due to
onset of puberty
changes

16. Lean to Fat Ratio
• Lean to Fat Ratio – the relationship between lean
muscle tissue and fat on an individual
• Intact males have the highest lean to fat ratios
• Heifers, ewes, and barrows have the lowest lean to fat
ratios
• Degree of marbling is inversely related to lean-to-fat ratio
• Carcasses with high lean-to-fat ratios have low degrees of
marbling
• Lean-to-fat Ratios effect animal evaluation and pricing due
to their relationship with marbling since marbling is a major
factor in quality grading and pricing
• Gilt is unique**

17. Lean to Fat Ratio cont.

18. Nutrition and Growth
• All essential nutrients are needed for animal to achieve optimal
growth and development of their tissues
• amino acids, protein, and energy
• Carbohydrates provide the major energy source
• 50-65% energy needed for maintenance
• Excess energy goes to fat
• Excess protein is wasted
• With limited protein, an animal’s muscle growth and gains are reduced as well as tissue
contribution
• Muscle is made up of water and protein!

19. Feeding Livestock
• Lean fat tissues and growing animals require more protein
• Runts have nutrient requirements limited by blood supply, deposit fat
earlier, and they never catch up
• Bucket calves**
• Intact males and late maturing males require more protein
• restricted energy during the growing period compared to full feed, fatter carcasses
• Protein quality effects finishing!

20. Evaluation Criteria
• Weight – the most common characteristic used for evaluation
• Muscle – used for live evaluation to determine the % muscle
composition of the animal using the leg, loin, ham, quarter, and stifle
• Fat
• Measured in cattle at the 12th rib, marbling
• Measured in sheep at the 12th rib on the left and right sides and averaged
• Measured in pork at the last rib at midline, and 10th rib at midline
• USDA at last rib,
• Marbling at 10th rib

21. Nutrition-Growth
• Beef Yield Grade – yield of boneless trimmed retail cuts from the
round, loin, rib, and chuck
• Sheep Yield Grade – yield of boneless trimmed retail cuts from the
leg, loin, rack, and shoulder
• Swine are evaluated using the percentage of lean cuts as well as the ham and
loin percentages
• All 3 of these are highly related to muscle over fat on a swine carcass