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 Reproductive Anatomy

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

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
– Early embryo development

Female Reproductive System infundibulum ovary 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)

Female Reproductive System

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

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

• Cow and ewe annular rings
• Sow - corkscrew
• Mare - longitudinal folds

• 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

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

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

Reproductive Functions (Female)
2. Estrus (heat)
– 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
Ewe
Goat
Sow
Cow
Mare
Length of
Estrous
Cycle
17 days
Duration of
Estrus
24-36 hours
21 days
21 days
21 days
21 days
32-40 hours
48-72 hours
18-19 hours
4-8 days
Time of ovulation
24-30 hrs from estrus onset
30-36 hrs from estrus onset
35-45 hrs from estrus onset
10-11 hrs after onset of estrus
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
Ewe
Sow
Hen
Mare
Goat calving lambing farrowing hatching foaling kidding calf lamb piglet chick foal kid

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

Male Reproductive Tract
• Scrotum - external sac that holds testicles outside of the body
– Maintains sperm 4-5 o F 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

Testicle Anatomy

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