Horse Reproduction & Parturition

Equine Science & Technology

Horse ReproductionReproductive organs of the stallion The primary sex organ of the stallion is the testicle, of

which there are two. The testicles produce sperm and A hormone called testosterone, which regulates and maintains

the male reproductive tract, and is responsible for the masculine appearance and behavior of the stallion.

Sperm production takes place within the testicles in the seminiferous tubules- a mass of minute, coiled tubules, the inner wall or surface of which produces the sperm.

Horse ReproductionReproductive organs of the stallion Theses tubules merge into a series of larger ducts, which

carry the sperm to a coiled tube called the epididymis. The epididymis is the place where the sperm are stored and

where they mature. The testicles and epididymis are enclosed in the scrotum,

the chief function of which is thermo-regulatory –to maintain the testicles temperatures several degrees cooler than the body proper.

Horse ReproductionReproductive organs of the stallion From the epididymis the sperm move through a tube, the

vas deferens, into the urethra. The urethra has a dual role; it carries:

Urine from the bladder through the penis, and Sperm from the junction with the vas deferens to the penis.

Along the urethra are the accessory sex glands- the prostate, the vesicular glands (seminal vesicles), and the bulbourethral (Cowper’s) glands. Their fluids nourish and preserve the sperm and provide a medium for its transport.

The combined sperm and fluid is called semen.

Horse ReproductionReproductive organs of the mare The primary sex organ of the mare is the ovary (2) The ovaries are bean-shaped organs, 2 to 3 inches long

that produce eggs. Each egg is contained in a bubble-like sack called a

follicle. There are hundreds of follicles on every ovary. When the follicle is about 1 in. in diameter a hormone causes it

to rupture and discharge the egg. This process is known as ovulation.

Horse ReproductionReproductive organs of the mare The egg is then trapped in a funnel-shaped membrane

called the infundibulum, which surrounds the ovary. The infundibulum narrows into a tube called the oviduct. The oviduct then carries the egg to the uterus, or womb,

the largest of the female reproductive organs. There the unborn young (the fetus) will develop.

Horse ReproductionEstrus Cycle Fillies generally start heat cycles at 12 to 15 months. The mare is seasonally polyestrous

Multiple estrous cycles only during certain times of the year. During the anestrous (nonovulatory) period, most mares

show no behavioral signs of sexual receptivity (estrus) and fail to develop follicles that ovulate.

Horse ReproductionEstrus Cycle In the Northern Hemisphere, the anestrous period of the

mare occurs most frequently during the winter. The estrous cycle is divided into two physiological parts:

estrous and diestrus. Estrus refers to the time the mare is in heat and sexually

receptive to the stallion.

Horse ReproductionEstrus Cycle Diestrus refers to the longest period (15 to 19 days) of the

estrous cycle; It is the time the mare is not receptive to the stallion. Mares do not always follow a cycle … they can be erratic.

Estrus usually lasts 3 to 7 days. Ovulation generally occurs 24 to 36 hours prior to the end

of estrus. The hormones produced by the hypothalamus, anterior

pituitary, and ovaries are responsible for both the release of the egg and the behavioral signs of estrus.

Horse ReproductionEstrus Cycle Estrogen- the primary hormone responsible for causing

the characteristic changes that occur in the mare’s genital tract.

Leutenizing hormone (LH)- the primary hormone responsible for ovulation. It is highest at ovulation.

Progesterone- a hormone which is produced in the corpus luteum. It is primarily responsible for the recognition and maintenance

of pregnancy.

Horse ReproductionEstrus Cycle Ovulation occurs in response to increased levels of LH. If the mare is not pregnant, the corpus luteum (CL) begins

to regress in response to prostaglandin. Progesterone levels decrease when the CL regresses.

Horse ReproductionEstrus Cycle Mares are long-day breeders, and thus the percentage of

ovulating mares increases significantly as the daily photoperiod increases above the 12-hour vernal equinox.

Generally, the maximum number of naturally occurring mares occurs during the maximum daylight periods of June.

Horse ReproductionCare of the pregnant mare The average gestation period of mares is 340 days, or a

little more than 11 months. Pregnant mares are often housed separately from other

horses. Pregnant mares should be closely monitored for any signs

of sickness or possible abortion. Mares should receive routine health care, including

worming, vaccinations, and care of the teeth and feet.

Horse ReproductionCare of the pregnant mare Which vaccinations are given depends on the farm and

location and should be determined after consultation with a local veterinarian.

Approximately ten days before the foal is to be expected, arrangements for the place of foaling should be completed.

During the spring, summer, and fall months when the weather is warm, the most natural and ideal place for foaling is a clean, open pasture away from other livestock.

Horse ReproductionArtificial Insemination Artificial Insemination (AI) is less widely practiced in

horses than in dairy cattle. AI:

Permits more mares to be bred to a stallion Makes for a higher conception rate Lessens the hazard of transmitting an infection or

a disease Lessens the risk of injury to the stallion or the mare.

Horse ReproductionKinds of Processed SemenThree kinds of processed semen are used in horses – fresh,

cooled, and frozen. Fresh semen- Fresh semen is collected, and an extender is

usually added. The semen may be stored in a refrigerator at about 55° F and used within 24 hours.

Cooled semen- Cooled semen is slowly cooled from body temperature down to 41° F. Cooled semen is usually viable for 24 to 72 hours, depending on the stallion.

Horse ReproductionKinds of Processed Semen Frozen semen- Following collection, an extender is added

to semen that is to be frozen. This semen can be stored indefinitely. The drawback is that pregnancy rates in horses using frozen semen are only approximately 35%.

Horse ReproductionEmbryo Transfer An embryo can be nonsurgically removed from the uterus

of one mare, transferred, and inserted into the uterus of another mare.

Embryo transfer allows reproduction by older, less fertile mares, reproduction by two-year-old mares, and increased production of foals from genetically superior mares.

This method is very expensive and the yield is not high.

Horse ReproductionCloning A cell, group of cells, or organism descended from and

genetically identical to a single common ancestor. In cloning, a cell is propagated from a host cell.

Horse ReproductionProper care during pregnancy and parturitionWhen rendering assistance to a mare that is about to foal the

following precautions should be followed: Cleanliness Quietness Gentleness Perseverance Knowledge, skill, and experience

Horse ReproductionProper care during pregnancy and parturitionIf foaling has been normal, the attendant should enter the stall

to make certain that … The foal is breathing The membranes have been removed from its mouth and

nostrils.

Horse Reproduction

Condition score is a method used to quantify the amount of subcutaneous fat cover.

The scale is 1to 9 1 = Poor/thin 9 = Extremely fat

If a mare is not in acceptable condition, her diet must be changed to move her in the direction of a five score.

Thin mares must gain weight since poor nutrition causes mares not to cycle normally.