Horse Reproduction &
Parturition
Equine Science & Technology
Horse Reproduction
Reproductive organs of the stallion
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The primary sex organ of the stallion is the testicle, of
which there are two.
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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 Reproduction
Reproductive organs of the stallion
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Theses tubules merge into a series of larger ducts, which
carry the sperm to a coiled tube called the epididymis.
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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 Reproduction
Reproductive organs of the stallion
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From the epididymis the sperm move through a tube, the
vas deferens, into the urethra.
The urethra has a dual role; it carries:
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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 Reproduction
Reproductive organs of the mare
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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.
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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 Reproduction
Reproductive organs of the mare
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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 Reproduction
Estrus Cycle
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Fillies generally start heat cycles at 12 to 15 months.
The mare is seasonally polyestrous
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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 Reproduction
Estrus Cycle
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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 Reproduction
Estrus Cycle
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Diestrus refers to the longest period (15 to 19 days) of the
estrous cycle;
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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 Reproduction
Estrus Cycle
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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.
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It is primarily responsible for the recognition and maintenance
of pregnancy.
Horse Reproduction
Estrus Cycle
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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 Reproduction
Estrus Cycle
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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 Reproduction
Care of the pregnant mare
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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 Reproduction
Care of the pregnant mare
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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 Reproduction
Artificial Insemination
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Artificial Insemination (AI) is less widely practiced in
horses than in dairy cattle.
AI:
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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 Reproduction
Kinds of Processed Semen
Three 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 Reproduction
Kinds of Processed Semen
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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 Reproduction
Embryo Transfer
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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 Reproduction
Cloning
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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 Reproduction
Proper care during pregnancy and parturition
When 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 Reproduction
Proper care during pregnancy and parturition
If 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.
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The scale is 1to 9
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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.