Reproductive Structures and
Cycles in Livestock

Terminology
• Reproductive cyclicity
– Provides females with repeated
opportunities to become pregnant
• Estrous Cycle
– Physiologic events that occur
between periods of sexual receptivity
and/or ovulations
• Estrus
– Period of female sexual receptivity

Terminology
• Castration
– Removing the testicles of the male
to prevent breeding
• Anestrus
– Condition when females do not
exhibit regular estrous cycles
• Gestation
– Time an animal is pregnant

Terminology
• Parturition
– The act of giving birth
• Lactation
– Period of time that milk is secreted
by the mammary glands
• Colustrum
– First milk containing a high content
of antibodies providing temporary
immunity to the offspring

The Female Reproductive
System
Objective: Identify the parts
of the female reproductive
system of livestock

Female Tract

Suspensory Ligaments
• Broad Ligament
– Supports and suspends tract
– Provides vascular supply
– Lymphatic drainage
– Nerves
• Composed of:
– Mesometrium (Body)
– Mesosalpinx (oviduct)
– Mesovarium (ovary)

Suspensory Ligaments

Ovary
• Female gonad comparable to the male
testicle
– Site of gamete production
– Bovine have 20,000 potential eggs (ova)
per ovary, humans have 400,000
potential eggs per ovary
– Ova are fully developed at puberty and
are not continuously produced as in the
male
– The hen has only a left functioning ovary

Ovaries Continued
• Suspended by mesovarium
• Shape varies by species
– Cattle-almond shaped
– Horses- bean shaped
– Sheep- round
– Swine- lobular

Ovaries of various species
Sow ovary
Ewe ovary
Cow ovary
Mare

Functions of the Ovaries
• Gamete production
• Secrete estrogen (hormone)
• absence of muscle development
• development of mammary glands
• development of reproductive
systems and external genitalia
• fat deposition on hips and stomach
(source of energy)
• triggering of heat
• Form the corpus luteum

Oviducts (Fallopian Tubes)
• Pair of small tubes leading from the
ovaries to the horns of the uterus
– Site of fertilization
– Supported by mesosalpinx
– 3 to 4 days for egg to travel down
oviducts
• Infundibulum - funnel shaped portion
of the fallopian tube that catches the
ovulated egg

Oviducts (Fallopian Tubes)
• Functions:
– Ovum transport
– Sperm storage and capacitation
– Fertilization (AI)
– Early embryo development

Female Reproductive System
ovary
infundibulum
uterus

Uterus
• Muscular sac connecting fallopian
tubes and cervix
• Consists of a body and two horns
– Cow, ewe, and mare (bicornuate)
– Sow has only horns, no body
– Woman has no horns (simplex)

Uterus Functions
• Sustains sperm and aids in its
transport
• Maternal placenta - supports embryo
and fetus during gestation
• Expels fetus at parturition
• Control of cyclicity

Female Reproductive System

Cervix
• Area between the uterus and vagina
• Normally closed; opens at estrus and
parturition
• Functions:
– Lubrication
– Flushing
– Barrier to foreign material or bacteria

Cervix – Species Differences
• Cow and ewe -
annular rings
• Sow - corkscrew
• Mare - longitudinal
folds

Vagina and Vulva
• Vagina: connects the
cervix to the external
genitalia and serves as
the female copulatory
organ
• Vulva: external tissue of
the female reproductive
tract, receives penis
during copulation

Female Reproductive System

Reproductive Tract of Cow

Sow

Reproductive Tract of the Ewe

Reproductive Tract of the Mare

Reproductive Functions (Female)
• Steps in the female reproductive
process:
1. Ovulation
— Produce gamete (ova or ovum)
— Release of egg(s)
— Infundibulum pushes the ovum into the
fallopian tube

Reproductive Functions (Female)

Ovulation Rates by Species
Species Ovulation Rate
Cow 1 egg/estrus
Ewe 1 - 3 eggs/estrus
Sow 10 - 20 eggs/estrus
Mare 1 egg/estrus
Hen ~ 28 eggs/month

Reproductive Functions (Female)
2. Estrus (heat, estrous period)
– Period of time when a female will accept a
male in copulation
– The female must stand (standing heat)
to be mounted before the reproductive
process can begin
– Estrus detection methods: visual
inspection, teaser animals, marker aids

Types of Cyclicity
• Polyestrus - uniform distribution of
estrous cycles occurring regularly
throughout the year
– Cow, sow
• Seasonal Polyestrus - “periods” of estrous
cycles occurring only during certain
seasons of the year
– Sheep, goat, deer, mare
• Monoestrus - only one cycle per year,
often lasting several days
– Dogs, wolves, bear, fox

Timing of Events in the
Reproductive Cycle
Species Length of
Estrous
Cycle
Duration of
Estrus
Time of
ovulation
Ewe 17 days 24-36 hours 24-30 hrs from
estrus onset
Goat 21 days 32-40 hours 30-36 hrs from
estrus onset
Sow 21 days 48-72 hours 35-45 hrs from
estrus onset
Cow 21 days 18-19 hours 10-11 hrs after
onset of estrus
Mare 21 days 4-8 days 1-2 days
before end of
estrus

Reproductive Functions (Female)
3. Gestation
— Fertilization to parturition
— Develop embryo in uterus
4. Parturition
— Expel fully developed young at birth
5. Lactation
— Milk production

Reproductive Terminology
Species Act Offspring
Cow calving calf
Ewe lambing lamb
Sow farrowing piglet
Hen hatching chick
Mare foaling foal
Goat kidding kid

Gestation and Lactation Periods
Species Gestation Period
(days)
Lactation Period
(days)
Cow 275 - 285 beef 180 - 270
dairy 305 - 365
Ewe 115 - 142 60 - 90 - 120
Sow 112 - 115 21 - 42
Mare 330 - 345 90 - 150
Woman 270 ? (years)

Reproductive Functions (Female)

The Male
Reproductive Tract
Objective: Identify
the parts of the male
reproductive system
of livestock and
poultry

Male Reproductive Tract

Male Reproductive Tract
• Scrotum - external sac that holds
testicles outside of the body
– Maintains sperm 4-5oF cooler than
the body temperature
• Testicles - primary male organs of
reproduction
– Produce sperm
– Secrete testosterone

Cryptorchidism
• Failure of one or both testes to
descend into the scrotum
– Unilateral: one testis does not
descend
•testis that descends is fertile;
reduced sperm concentrations
– Bilateral- neither testes descend into
scrotum
•Results in sterility due to elevated
temperature of both testes

Male Reproductive Tract
• Epididymis: long coiled
tube that is a path for
sperm
– Provide passageway for
sperm out of the
seminiferous tubules
– Storage for sperm
– Fluid secretion to nourish
sperm
– Place for sperm maturation

Male Reproductive Tract
• Vas Deferens - slender tube from
epididymis to urethra
– Moves sperm to the urethra at
ejaculation
• Urethra - long tube from bladder to
penis
– Passageway for urine and sperm
out of the body

Male Reproductive Tract
• Penis - male organ of copulation
which conveys semen and urine out
of the body
• Penis retractor muscle - allows
extension and retraction of the
penis; sigmoid flexure extends in
copulation

Fibroelastic vs. Vascular Penis
• Fibroelastic: erection extends the length
of penis rather than diameter
– Bull, Ram, Boar
• Vascular: composed of specialized
tissues that fill with blood causing the
penis to become turgid during erection
– Stallion

Male Reproductive Tract
Accessory Glands:
• Seminal vesicles- add fructose and
citric acid to nourish the sperm
• Prostate Gland - located at the neck of
the bladder
– Cleans the urethra prior to and
during ejaculation
– Provides minerals for sperm
– Provides the medium for sperm
transport
– Gives semen it’s characteristic odor

Male Reproductive Tract
• Cowper’s gland
•Also called the Bulbourethral
gland
•Paired organs
•cleans the urethra prior to semen
passage

Male Reproductive Tract

Differences in Tracts
• Bulls- Pendulous, perpendicular testes
• Ram- Pendulous, perpendicular testes;
Filiform appendage
• Boar- Inverted testes; No ampulla;
corkscrew penis; much larger
bulbourethral gland
• Stallion-Horizontal testis; loosely
attached tail of epididymis; Smooth
seminal vesicles; no sigmoid flexure

Bull Reproductive Tract

Ram Reproductive Tract

Boar Reproductive Tract

Stallion Reproductive Tract

Reproduction in
Poultry
Objective: Specify how the
reproductive system for
poultry functions

Reproduction in Poultry
The poultry oviduct has five parts:
1) Vagina
– Holds the egg until laid
2) Uterus
– Secretes the shell
3) Isthmus
– Adds the two shell membranes
4) Magnum
– Secretes the albumen
5) Infundibulum
– Where fertilization takes place

Reproduction in Poultry
• Major difference:
– Embryo of livestock develop inside the
female’s body while the embryo of poultry
develops inside the egg.
• Poultry only have the left ovary and
oviduct when mature
• The yoke is the ovum
• Chicken Incubation
– 21 days