Equine Reproduction
LESSON ONE
Anatomy and Physiology of the
Stallion
This lesson does not have a
corresponding chapter associated with it. No reading assignment will be given
in lesson one.
EQUINE REPRODUCTION – TERMS
Introduction of Terms and Facts
During this course you will be
exposed to many new vocabulary words that are commonly used in the breeding
industry, but with which you may not be familiar. It is important you have a working knowledge
of these terms in order to more efficiently function in an equine breeding
environment.
Stallion Terms
Anabolic
steroid or hormone:
Androgenic hormone derived from testosterone.
Aggression and increased libido.
Breeding
roll: Usually made as a roll
of cotton on a pole which is placed between the mare’s hind quarters and the
stallion (above the penis) to prevent the stallion from deep penetration during
breeding. (maiden mares, mares with caslicks)
Bull
Pole: A sturdy pole that can
be fastened to the halter to keep an aggressive stallion from crowding the
handler.
Cryptorchid: A male
horse in which one testicle is retained in the body cavity.
Ejaculation: Emission of
semen from the penis.
Flaccid: Refers to a non erect penis in the stallion.
Flehman: Common
behavior pattern consisting of curling and raising of
the upper lip indicating sexual stimulation in the stallion.
Libido: Sexual
drive or desire.
Scrotum: Pouch that
contains the testicles.
Spermatogenesis: Development
of mature sperm cells which occurs within the testicles.
Stallion
ring: Rubber or plastic ring secured behind the
glans penis of the stallion that discourages stallion erection.
Teaser: A male horse
used to detect estrus (heat) in mares.
Vasectomy: Operation in
which the vas deferens is cut to prevent passage of sperm from the testicle
into the male repro tract.
Broodmare Terms I
Abortion: Expulsion of
the fetus from the uterus between 30 and 300 days of gestation.
Early
embryonic death: Expulsion of the embryo or absorption of the
embryo from conception to 30 days of pregnancy. (absorption
or resorption)
Afterbirth: Expelled
placenta.
Agalactia: Absence of
milk in the udder after foaling.
A.I.: Artificial
Insemination.
Anestrus: Period of
sexual quiescence. No estrous
cycle. Winter months.
Cervical
os: Opening of the cervix.
Conception: The meeting
of the sperm and the ovum to form the embryo. In the mare this occurs in the
oviduct.
Corpus
luteum: the primary
source of ovarian progesterone, which normally increases after ovulation. CL forms
after ovulation and is usually functional for 14 to 15 days in the nonpregnant mare. Corpora lutea
that fail to regress at the normal time postovulation
are considered to be pathologically persistent.
Fertilization: The union of the sperm and the ovum.
Gestation:
Pregnancy.
Hymen: The thin
membrane that partially covers the external vaginal opening, found in maiden
mares.
LH: luteinizing
hormone. – Causes follicle ovulation and formation of CL
Luteolytic:
Causing the lysis or
degeneration of the CL. (prostaglandins) (Luteolysis)
Maiden: A mare that
has not been bred.
Ovulation: The release
of the ovum (egg) from the mature follicle.
Silent
heat: Estrus period in which the mare ovulates, but
fails to show behavioral signs of heat.
Speculum: Instrument
for enlarging the opening of a cavity as in vaginal speculum.
Transition
phase (transitional anestrous): The period that occurs at the beginning of the
breeding season, marked by erratic estrous cycles.
Winking: A behavioral
sign from a mare in heat, turning and lifting the tail and everting the vaginal
labia to expose the clitoris.
Broodmare
Terms II (The pregnant mare)
Gestation
period: 11 months and 7 – 11
days.
Days in
estrus (heat): 5 days
Ballottement: A method of
pregnancy diagnosis in which the uterus is tapped through the rectum or flank
and the fetus can be felt bouncing back against the hand.
Breaking water: Expulsion of fluids from the uterus prior to the
foal being passed.
Breech
birth: The hindquarters are presented first during
foaling.
Breeding
stitch: Heavy suture placed at the lower end of the caslicks’ suture line to reinforce the suture line during
breeding.
C
section: caesarean section –Surgical removal of the
fetus.
Dystocia: Abnormal or
difficult birth.
Endometrial
cups: Raised structures formed at about day 36 of
pregnancy and responsible for progesterone release and maintenance of pregnancy
up to 120 days.
Foal
heat: The first heat or estrus period after
foaling (9-day heat).
Hobbles: Device used
to restrain an animal by restricting leg movement.
Involution: In the
mare, the process by which the uterus returns to the normal state after pregnancy.
Kicking
Boots: Padded boots sometimes placed on the mare’s
back feet to reduce any blow sustained by the stallion during breeding.
Lactation: The period
of milk production.
Palpation: Feeling by
the sense of touch – rectal palpation of ovaries and uterus.
Placenta
(afterbirth): Tissue which surrounds the fetus during
pregnancy. It is connected to the fetus by the umbilical cord and serves as the
structure by which the fetus receives nourishment from and eliminates waste matter
into the maternal circulatory system.
Postpartum: Pertaining
to or after the birth of the foal.
Resorption: The
absorption of an early pregnancy – Early embryonic death.
Retained placenta: Afterbirth
that is not expelled within 4 to 6 hours after foaling.
Stillbirth: the birth
of a dead fetus.
Waxing: Formation
of beads of dried colostrums at the ends of the teats.
Hormones Associated with Reproduction
|
Hormone |
Primary Production site |
Target organ |
Effect |
Therapeutic use |
|
Estrogen - Heat hormone |
Ovary (ovarian follicle) |
Uterus, cervix, and external genetalia of mare |
Expression of
estrus. Female sex
characteristics, genital tract changes |
Enhances estrus (heat) but may
interfere with normal cycling. |
|
Progesterone -Pregnancy Hormone |
Corpus luteum of ovary (CL) also
the placenta during pregnancy |
Uterus Mammary gland |
Maintains pregnancy |
Prevent abortion. Synchronize or
suppress estrus (regumate) |
|
Prostaglandin |
Uterus |
Corpus Luteum (CL) |
Luteolysis.(CL regression) |
Synchronize estrus. Treat
persistent CL. |
|
Gonadotropin releasing hormone
(GnRH) |
Hypothalamus |
Pituitary gland (master gland) |
LH and |
|
|
Follicle Stimulating Hormone( |
Pituitary gland |
Ovary-mares Seminiferous tubules-male |
Growth of follicle-mare
spermatogenesis-male |
Same as effect |
|
Luteinizing Hormone (LH) |
Pituitary gland |
Mature follicle–mare Leydig cells –male |
Follicle maturation and ovulation Stimulates testosterone
production |
Same as
effect. (gonadotropin(HCG) |
|
Oxytocin |
Pituitary gland |
Uterus , mammary gland |
Uterine contraction, milk let
down |
Retained placenta elimination,
induce abortion or foaling |
|
Prolactin |
Pituitary gland |
Mammary gland |
Milk production |
|
|
Relaxin |
Ovary, placenta |
Pelvic tissues |
Relaxation of pelvic area for
foaling |
|
The Foal
and Foaling Mare terms
Agalactia: Absence of
milk in the udder after foaling.
Colostrum: The first milk
of the mare rich in protective antibodies.
Congenital: Existing at
and usually before birth. May or may not
be inherited.
Coprophagy: Manure ingestion.
Feral: Not
domesticated.
Fetus: The unborn
foal from 40 days to birth.
Foal
heat diarrhea or scours: Diarrhea that usually occurs in foals during
the mares foal heat.
Gonad: Organ that
produced gametes (testicles or ovaries).
Live
foal guarantee: Stallion contract provision that guarantees the
mare owner a live foal as a result of the purchased breeding. The guarantee
usually gives the mare owner the right to rebreed the next season to the same
stallion.
Meconium: The first
fecal passage of the newborn.
Neonate: Foal less
than 3 or 4 days of age.
Nurse
mare: A mare selected for mothering ability and
bred each year for the purpose of raising orphan foals.
Suckling: An unweaned foal.
Urachus: Small
vessel in the umbilical cord that connects the fetal urinary bladder to the
outside.
Weaning: To
permanently deprive of milk.
Early
embryonic death: Expulsion of the embryo or absorption of
the embryo from conception to 30 days of pregnancy. (absorption
or resorption).
The Infected Mare
Agar: Culture
media used for growing bacteria.
Barren: A mare
(other than a maiden mare) that did not become pregnant during the last
breeding season. (Dry mare).
Caslicks operation: The process
of stitching the upper 1/3 to ˝ of the vulvar lips together to prevent
wind-sucking ( the sucking of air or contamination
into the reproductive system of the mare.
Culture
and sensitivity: Taking of a swab from the uterus of the mare
and attempting to grow bacteria to determine infection then subsequently determining
to what antibiotic the growing bacteria will be sensitive. (would
be effective in combating the infection).
Endometritis
(metritis): Inflammation or infection of the uterus.
Fertile: Able to
produce offspring.
Gonadotropin
– gonadotrophic: A hormone that promotes gonadal growth and
function.
Impotency: In the
stallion, the reduced ability, inability, or lack of desire to breed.
Infertility: In the
stallion - the reduced ability of the sperm to fertilize the ovum or the
reduced ability of the stallion to produce sperm. In the mare - the
reduced ability or inability of the mare to conceive or carry a foal to term.
Metritis:
Inflammation or infection of the uterus.
Open: Not
pregnant.
Resorption: The
absorption of an early pregnancy – Early embryonic death.
Artificial
Insemination and Embryo Transfer
A.I.: Artificial
Insemination.
AV: artificial
vagina – Used to collect semen from the breeding stallion.
Autoclave:
Sterilization device that uses pressurized steam to sterilize
instruments.
Catheter: Hollow
cylinder designed to introduce fluids into a body cavity.
Condom: Sometimes
used for collection of semen from the stallion.
Dismount
sample: the portion of the stallion’s ejaculate which
trickles from the penis immediately following dismount from breeding. Sometime used for semen evaluation although
not very reliable.
Donor
mare: The mare which donates an embryo for embryo
transfer. (The more valuable mare).
Recipient
mare: The mare receiving the donated embryo to
carry through pregnancy to term.
Embryo: Considered
to be the union of the sperm and ovum up to 30 to 40 days of pregnancy.
Embryo
Transfer: A method whereby a developing embryo is
removed from its natural mother and implanted in the uterus of a host mother
for the remainder of pregnancy.
Estrous
synchronization: Process by which two or more mares are
synchronized so they come into heat (estrus) at the same time. Used most often
in embryo transfer, prostaglandin or progesterone (regumate)
is the drug used most effectively for this process.
Extender: Liquid
formula used for semen dilution and longevity.
Hemospermia: The
presence of blood in the semen.
Phantom
or dummy mare: A raised, padded support that is mounted by
the stallion for semen collection.
Semen: The
ejaculate comprised of sperm cells and secretions of the testes and accessory
sex glands.
Spermicidal: A substance
that would inactivate or kill sperm cells if that substance comes into contact
with semen.
Sperm
rich fraction: That portion of the ejaculate which contains
80-90% of the ejaculates total number of sperm.
The
Stallion Reproductive System
I.
Anatomy & Physiology
(structure and function of the stallion reproductive system).
a. External
Genitalia
1. Testis
(Testicles) (2) – Are found within the
scrotum, and have a dual function. The testicles are considered both an
exocrine gland (produces a cellular component that is transferred through a
duct system) and an endocrine gland (produces a hormone that is absorbed through
the blood stream and carried throughout the tissues in the circulatory system.)
The exocrine function of the testicles is the production of sperm cells. Sperm
cells are produced within the testicular tissue and require a slightly cooler
environment that normal body temperature. The scrotum acts as a thermo
regulator in that it is able to keep the testicles away from the body and
therefore the temperature of the testicular tissue is conducive to the
production of live sperm cells. The cremaster muscle, which attaches to the
each testicle is also a part of the thermoregulatory system and can contract
and pull the testicles up closer to the body during colder weather, and relax
and drop the testicles further from the body in warmer weather, thereby
guaranteeing live sperm production. The pampiniform plexis, a convolution of blood vessels supplying the
testicular tissue with blood, is also part of the thermoregulatory system, in
that it cools the blood going to the testicles. The endocrine function of the
testis is the production of the male hormone testosterone. Testosterone, the
male hormone, initiates sperm production and development and maintenance of
masculine characteristics and is also responsible for the libido (sex drive or
sexual desire).
The Epididymis connects the
testicle to the vas deferens. The
epididymis is
where sperm is stored. The vas
deferens (deferent
duct or
ductus deferens) is the channel by which the sperm are
transported
from the epididymis to the urethra during ejaculation.
The Urethra is surrounded by the
Penis and is responsible for
transporting
sperm to the mare’s reproductive tract.
The Prepuce (sheath) surrounds and
protects the penis.
Other internal sexual organs of importance
are the accessory sex glands (Seminal Vesicles, Bulbourethral gland, prostate
gland and the ampulla) which
add fluid volume and nourishment to the sperm cells.
(Pre-ejaculate, ejaculate, gel fraction, tail end fraction of a semen sample)
Here
students at an Equine-Reproduction.com course watch as a ground collection is
demonstrated.
More
details of this technique can be found in the article at
http://www.equine-reproduction.com/articles/ground_collection.shtml
Photographs are used with permission of Equine-Reproduction.com LLC and may not be reproduced.
Erection and ejaculation are brought
on by psychic stimulation of the brain usually brought on by a mare in
heat. Here students collect a stallion.
b. Penis
engorges with blood which causes a rigid penis with an increase in length of
about 50%.
c. Ejaculation
– expulsion of semen from the penis. Ejaculation consists of about 10
pulsations that occur at approximately one second intervals. About 75% of the
total sperm is present in the first
Puberty (attain the ability to breed
a mare) usually occurs in the light breed horses of
Testosterone
caused male sex characteristics include:
1. Increased muscling of the neck, head,
shoulder
and back.
2. Closure
of growth plates of the long bones (epiphysis).
3. Onset
and maintenance of normal sex drive.
4. Sperm production.
5. Sex drive (libido)
and aggressiveness. (Flehman response – curling
of the upper lip).
Sex
drive is an inherited trait that determines how quickly the stallion can be
trained for breeding shed procedures, and also determines how stable his
behavior will be after training. The act of breeding, in contrast, is a trial
and error - learning process.
A stallion “teasing” a mare.
The individual
sperm anatomy
i.
Head, neck piece, mid piece,
tail.
ii.
Must be seen microscopically in
the horse to determine normal anatomy and motility. (Motility of bull semen can
be determined without a microscope.)
We will go into greater detail and
study of sperm cell anatomy and physiology in the lesson on Artificial
Insemination.
Stallion
Management
I.
Stallion Selection -
a. Genetic
potential – quality traits that can be passed on to his offspring.
b. Willingness
to cover mares and physical ability to settle them. (Individual libido and
fertility.)
II.
Reproductive Exam
A. Experienced
veterinarian or equine reproduction specialist.
1. Overall
general health exam.
2. Medical
history.
3. Disposition
(libido).
4. Physical
exam of reproductive anatomy.
5. Physiological
exam involving observation of the breeding process as well as semen evaluation.
a. Volume
of semen per ejaculate.
b. Concentration
of sperm in semen.
c. PH
of semen.
d. Motility
of sperm cells.
e. Morphology
of sperm cells.
f. Live
– dead percentages.
g. Longevity.
h. Contamination
(wbc’s or rbc’s present).
Normal Semen Parameters
Volume
30-250 ml.
Concentration
– 30-600 million (10 to the 6th) /ml.
PH – 6.9 to
7.8
Morphology
– at least 65% normal.
Live/dead
count – at least 65% live cells.
Motility
– at least 40% actively motile (moving in a straight line).
Longevity – at
least 40-50% live after 3 hours at room temperature; at least 10% live after 8
hours at room temperature.
III.
Stallion Vices
A. Vices
dangerous to the handler or mare:
1. Overly
aggressive behavior (savaging mares or handlers).
2. Biting
(muzzle or protective leather pad for mare).
3. Rearing
and striking (nose chain or lip chain).
B. Vices
dangerous to stallion.
1. Self
mutilation (muzzle or neck cradle; increased exercise or companion.)
2. Cribbing
and windsucking (cribbing strap). A diet
with no long stem roughage can lead to wood chewing.
3. Weaving
and stall walking (exercise or obstructions in the weaving or walking path
and/or a companion).
C. Vices detrimental to breeding.
1. Slow
breeder (need for extended stimulation for erection and mounting or repeated
mounts to ejaculate).
a. Improper
breeding training.
b. Abusive
or rough handling.
c. Overuse
of the stallion.
d. Prior
bad experience in the breeding shed.
2.
Masturbation
a. Boredom
– exercise or prevent the isolation of the stallion.
b. Stallion
ring or wire brush on belly.
IV.
Proper Stallion Management
A. Nutrition.
B. Exersise.
C. Housing.
D. Health
care.
1. Dental
care.
2. Preventive
medicine.
E. Hoof
care.
Normal
Number of
mounts per ejaculate – 1.5
Average
time to mount-- 5 seconds to 3 minutes.
Average
time to ejaculate-- 20 seconds to 1 minute.
Breeding time
(from onset of sexual stimulation to completion of breeding) – 45 seconds to 5
minutes.
Number of covers
per season—40
Percentage of
mares pregnant-- 65 to 90%
Percentage of
mares actually foaling – 45 to 80%
Stallion
Infertility
DEFINITIONS:
Infertility: reduced ability of stallion to impregnate a
mare.
Sub-fertility: same as above.
Sterility: complete and permanent loss of
the sperm’s fertilizing capacity or of the stallion’s ability to produce sperm.
Impotency: term used to describe the stallion’s reduced ability,
complete inability, or lack of desire to perform the breeding act.
Causes of
Infertility in the Stallion:
I.
Drugs
a. Testosterone
and /or anabolic steroids.
1. With
long term or excessive use these drugs will inhibit the normal negative
feedback system in such a way to inhibit the normal production of Interstitial
Cell Stimulating hormone (LH) and Spermatogenesis Stimulating Hormone (
b.
Other drugs, especially ones causing severe side effects such as diarrhea, loss
of
appetite or an
allergic reaction, could be a cause for infertility in the stallion.
II.
Overuse
a. Overuse is a potential cause of infertility
and impotency.
1. Young
stallions are more prone to overuse.
Daily breeding
in the average, aged stallion will lower the concentration of the stallion
sperm per ejaculate, but should not lower the total number of sperm produced
per day. (Generally leads to higher volume of sperm, with fewer sperm per milliliter
of semen).
Every other
day breeding in the average, aged stallion will not decrease the
concentration of the sperm produced at each ejaculate.
In an A. I.
operation, every other day collection is ideal.
In live cover
operation with full book of mares, although it depends on the individual
stallion, the average, aged stallion should be bred no more than 6 – 8 times a
week.
III.
Painful Breeding
A. Injuries
to the limbs, especially hind limb problems (hock or stifle lameness’s) may
cause the stallion to hesitate or refuse to breed.
Medication
and/or corrective shoeing may be necessary to manage the injury.
B. Painful
problems associated with the reproductive organs. Injuries to the penis.
Care must be
taken when using stallion rings, and when washing and handling the penis before
and during breeding and collection.
C. Excessively rough handling of the stallion,
or an uncooperative mare.
1. Behavioral
problems must be addressed efficiently and without causing more behavioral
problems.
IV.
Season of the Year
A. Stallion
is also affected by length of daylight.
1. During
the fall and winter months the stallion will have a longer reaction time,
longer time from initial sexual stimulation and mounting, and will have a
greater number of mounts required per ejaculation. (Libido decreases during
this time).
2. Semen
quality will be slightly less during this time.
V.
Genetic Aspects
A. Behavioral
as well as physical characteristics for sufficient breeding ability or
potential is genetically endowed.
B. Hormonal
abnormalities can be genetically endowed.
C. Cryptorchidism
–Failure of one or both of the testes to descend into the scrotum.
VI.
Diseases
A. Hereditary
disease associated with the reproductive organs.
B. Testes.
1. Orchitis
–infection or inflammation of the testicle can be caused by a number of
infectious diseases.
2. Tumors
– can occasionally affect one or both testicles.
3. Trauma
by physical blow (mare kicking) will affect fertility negatively.
C. Penis
1. Irritation
or localized infections could be a problem.
2. Tumors
(melanoma, or squamous cell carcinoma) will affect
fertility negatively.
D. Urethra
1. Infection
can be introduced from an infected mare into the stallion’s urethra and cause
the stallion to become infected. This infection can travel to the accessory sex
glands, the vas deferens, the epididymis and the testicle itself.
a. A
healthy stallion can usually resist this infection from becoming permanent, but
will be able to transmit to other mares during live breeding or A.I. until his
immune system clears it from his system.
VII.
Trauma
A. Physical
trauma to the external genitalia is probably the most common problem seen in
the stallion causing a temporary infertility or impotency during the breeding
season.
1. Breeding
shed accidents.
a. Best
prevented by good management and anticipation of possible problems. Use of
hobbles, routine breeding shed activities, proper stallion handling)
b. Penile
hematoma –
1. Blow
to the penis or bending of the penis while it is erect will cause a rupture of
the blood vessels within the tissues of the penis.
VIII. Semen
Abnormalities
A. Volume
– normally not a critical issue with fertility. Concentration (number of sperm
per ml. of semen, is the determining factor in fertility of the stallion).
B. Color
– Blood in semen renders the semen useless. (Blood or pus in the semen causes
infertility). Pus may also discolor the semen, and would indicate infection
within the reproductive tract.
C. Density
– Semen that is too thick and gelatinous or to thin and watery indicates
malfunction of the accessory sex glands.
D. Motility
– If collection and handling techniques did not cause the reduced motility,
some problem within the stallion is to blame. This would cause infertility if
found to be less than 50% progressively motile sperm in the sample.
E. Longevity
– If not caused by collection and handling techniques reduced longevity of the
sperm will reduce the sperms chances of fertilizing the mare’s ovum.
F. Morphology
– Abnormal sperm cells. Semen samples that contain less than 65% normal sperm
cells are directly related to reduced fertility.
G. Live/Dead
Percentage - If a semen sample contains less than 60% live cells in a fresh
sample, fertility may become affected.
H. Sperm
numbers – The reduction in the number of viable sperm cells per ejaculate may
be due to seasonal variation, overuse, testicular degeneration, or increased
testicular temperature. Sperm Concentration normally ranges from 30 million to
600 million sperm per milliliter, and at least 100 million progressively motile
sperm are needed for acceptable conception rates. The average concentration of
a stallion is 50 – 250 million per ml.
I. PH
– An increase in the semen ph (normal is 7.0 –7.8) may be caused by presence of
urine or by infection within the reproductive tract, or by overuse.
J. White
blood cells – Although some white blood cells may be found in a semen sample, a
greater than 1500 WBC per cubic milliliter) usually reflects infection within
the reproductive tract and infertility.