STALLION MANAGEMENT
Lesson Three
FERTILITY
You have found the stallion of your
dreams. He has the desirable pedigree, conformation, disposition, and a winning
record. The price seems to coincide with the prevailing market value for a
potential breeding stallion of his caliber.
The only thing that makes this stallion as
valuable as his price would indicate is his potential ability to successfully
stand at stud; meaning he would be expected to breed and impregnate an average
book of mares in a breeding season….. so you want his
fertility guaranteed.
What constitutes fertility is a gray
area: there are many evaluations, both qualitative and quantitative, that may
be used to give an educated appraisal of a horse's breeding strength.
Throughout history, the best way to
determine fertility of a given stallion prospect would be to test breed him to
3 to 5 fertile young mares. If the stallion gets a reasonable percentage of
these mares pregnant (65 to 90%) after one to 2 breeding cycles he would be
deemed fertile.
During the last 20 or so years it has
become acceptable to do a semen evaluation on potential stallions by collecting
a full ejaculate by way of an artificial vagina. A number of
semen quality and quantity parameters can then be compared to what is
considered normal or average, and fertility is verified.
Equipment necessary to set up a small
semen evaluation lab includes a microscope for viewing the individual male
sperm and its movement. The microscope does not have to be powerful or
expensive to do a decent fertility exam, but it needs to have a magnification
of at least 10 x 40 with fair resolution. Some sort of graduated container will
also be needed to measure volume, which is the first measurement taken on the
stallion's output of semen.
Microscope
When the ejaculate is collected, three
fractions are produced: the pre-wash, the sperm-rich fraction, and the
gelatinous plug. The sperm-rich fraction is the part with which we are most
concerned.
Collecting in a clear baby bottle with
a filter can provide a rough estimate of the volume. The filter stops the gel
fraction from entering the baby bottle and thus allows ease of evaluation of
the sperm rich fraction. Using this
system, we do not actually measure the gel fraction as part of the total
volume, but the importance of the gel fraction is only valid during natural
cover as a cervical plug to prevent backwash of the sperm rich fraction from
the uterus of the mare. If the gel fraction is mixed with the sperm rich
fraction it makes the actual semen evaluation procedure very difficult if not
impossible.
The first evaluation is the volume of
this part of the ejaculate. A range between 25 and 250 cubic centimeters is
normal for light horse breeds, with most ejaculates being around 100 cc. (Draft
breeds average around 400 cc.) When a stallion is collected on a regular basis
(every other day for example) the volume will level out at a lower amount
(usually around 35 to 60cc (ml) and the concentration will level out to a
higher concentration as well.)
Within the species there is an inverse
relationship between volume and the next parameter: sperm concentration.
Concentration is reported as the number of spermatozoa (sperm cells) in
one cubic centimeter (cc or ml) of semen. In general, as the volume increases,
the number of cells found in one cubic centimeter of semen decreases. The
normal range is 50 to 350 million sperm cells per cc with the mean being about
200 million sperm per cubic centimeter.
The educated eye of someone practiced in
evaluation of sperm concentration can be accurate to within 25 x 106
cells per cc by looking at a sample in the field of view of a microscope. An
ejaculate that has a milky blue color has a higher concentration of sperm
cells/cc than one that is marginally translucent.
For pinpoint accuracy of concentration
evaluation, which would be expected for evaluation of a valuable stallion, a hemocytometer
or spectrophotometer would be used. A hemocytometer which is used to
count red blood cells, can be adapted to count sperm cells. The hemocytometer
is simply a grid-marked slide. Count a certain number of grids multiple by a
factor and you have an estimate of the concentration of the ejaculate. This
technique, as with the experienced eyeball technique, results in a sample error
around 25 x 106.
Hemocytometer
More precision may be obtained using
spectrophotometry. This method provides a reading of the density of a fluid by
measuring how much light can pass through the medium. While this is the most
accurate measurement of concentration, it does require the machine be
calibrated for sperm cell density; and the price of the machine demands a large
number of samples to make the test cost-effective. Such equipment is usually
available at most horse breeding facilities that utilize artificial
insemination as their method of breeding mares. (Quarter horse, Arabian, Paint
horse breeding farms).
Spectrophotometer
However to be accurate in determining
the number of mares that can be bred with an ejaculate concentration is
an important number. For a farm that is trying to maximize the number of mares
that can be bred, knowing concentration is a must.
On the other hand
for a breeder with a proven stallion who only has 2 to 4 mares to breed, not
knowing the exact concentration usually doesn’t matter.
Also evaluated under the microscope is the
third characteristic of semen analysis: motility. Motility is an estimate of how many
cells out of a sample of 100 show life by movement in a relatively straight
line. Most fertile horses have motility that ranges from 40 to 70 per 100. Said
another way, these horses have between 40 and 70% motility.
The way these cells move is the fourth
characteristic. Subjectively, graded under a microscope, 10 individual sperm
are watched for their individual “swimming” ability. How many are traveling
forward, in a relatively straight line, are compared to the ones that are not
moving forward. If you have 7 out of 10 moving properly, you have a 70%
progressive motility. It is normally done on 3 sets of 10 in a sample and then
the average is taken from those three sets. This particular evaluation is
considered by some to be one of the most critical in determining breeding
potency.
The sperm cells of a fertile stallion
are expected to have a progressive motility of 40 to 80%.
The fifth examination is performed on
the morphology of the cells to discover how many of the spermatozoa are
misshapen. Horses have a slightly larger percentage of cells with irregular
morphology than other domestic animals.
Normally, up to 25% abnormal cells can
be tolerated in a stallion without cause for concern, but remember that an
ejaculate needs to be evaluated in terms of all of the criteria.
. 
Morphology of Stallion Spermatozoa
The sixth test, known as the livability
(viability) test, requires the ejaculate to be extended and then stored in a
refrigerator. This is an important factor in determining whether a particular
stallion could be used successfully in an Artificial Insemination program where
cooled semen is shipped to distant locals by air and mares are bred by AI
within a 24 to 48 hour period. Viability can also be meaningful on the semen
sample that is not extended and left at room temperature in the laboratory
where it is checked hourly over a 12 to 24 hour period.
Additional laboratory
equipment is also required to perform the eighth test. The semen is cultured in
a laboratory by streaking it on blood agar and other bacterial growth media, to
determine the presence of bacterial pathogens in the ejaculate. Many bacterial pathogens such as e.
coli, streptococcus, staphylococcus and pseudomonas
can be found and determined as to their actual pathogenic potential. The
presence of these organisms can adversely affect the fertility of a stallion,
even though the horse seems to be a strong breeder.
A stallion testing positive for such
pathogens provides a higher risk of introducing these organisms into the
reproductive tracts of the mares he breeds. Although bacteria such as
staphylococcus and pseudomonas are easier to control in the mare than in the
stallion (given the techniques and drugs available today), it is still an
expensive and tenacious malady to deal with - one that all mare and stallion
owners would certainly want to avoid. Fortunately this is one parameter that
can be corrected with proper antibacterial therapy prior to use as a breeding
stallion.
There are still other factors to be
aware of when performing a fertility examination, even though they rarely
occur. Blood in the semen (hemospermia) will
seriously limit the fertility of a stallion. Blood is lethal to spermatozoa and
also indicates a problem in the urogenital system. Urine leaking into the semen
during ejaculation is definitely cause for concern.
Urine is also a lethal substance for sperm cells and almost always causes total
sterility. Normally urine contaminated semen is seen in very old ( 20 years and older) stallions due to the aging process,
but occasionally cases have been reported in younger stallions.
Clumping of sperm cells is also an indicator
of poor fertility. The nucleus of the spermatozoa has an electrically charged
surface that causes it to be attracted to particles of an opposite charge. This
phenomenon is commonly seen under the microscope when dirt and debris
contaminate the sample.
Under the microscope, large numbers of sperm
cells will be found attached to the surface of the substances, thus
"clumping." When clumping occurs in samples free of contaminants, the
horse is likely to have a major reduction in fertility. It has been suggested
that the cause of this clumping may be a result of injections of steroids.
Whether there is any validity to this idea or not, it is certain that large
doses of steroids such as cortisone compounds or anabolic steroids, do reduce
fertility. While removal of these compounds from the animal's system should
allow for the return of fertility, the length of time it takes to reestablish
quality sperm production is also unpredictable and may take up to a year or
more. Therefore, before purchasing a stallion for breeding, it becomes very
important to have a history of his medications.
One of the more famous examples of
this situation involved the Thoroughbred racehorse Secretariat who, during the course of his racing career, received
cortisone to reduce inflammation. There were also rumors that he may have been
on performance enhancing anabolic steroids for a period of time. While this
outstanding athlete was in the process of winning the Triple Crown (Kentucky
Derby, Preakness Stakes, Belmont Stakes), he was syndicated for a large sum of
money for stud duty at the termination of his career. The syndication agreement
required that the horse must be able to pass a fertility examination at the
animal clinic of a major eastern veterinary school. Collection of this horse's
semen specimen did not put the purchasers' minds to rest, as the evaluation
showed the horse to have marginal fertility.
It was suggested, however, that this
marginal fertility might be attributed to the exogenous steroids prescribed for
the stallion. It was said that this calmed the fears of the buyers and they
didn't ask for their money back. Secretariat was test bred to an Appaloosa
mare, who promptly conceived and subsequently foaled a spotted stud colt.
Noteworthy of Secretariat’s offspring, is that fact that although Secretariat
never seemed to produce any superior race horses from his first generation of
offspring, He became known as a producer of superior broodmares (Mares sired by
him that ended up producing superior race horses). He also bred many
of the best Thoroughbred mares in the world until his untimely death from
founder (laminitis)
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. 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 (FSH) which
will in turn cause a reduction in sperm output, sperm motility, and testicular
size.
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 more prone to overuse.
2. 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. (leads to higher
volume of sperm, with fewer sperm per milliliter of semen).
3. Every
other day breeding in the average-aged stallion will not decrease the
concentration of the sperm produced at each ejaculate.
4. In
A. I. operation, every other day collection is ideal.
5. 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.
1.
Medication and/or corrective shoeing may be necessary to manage the injury.
B. Painful problems
associated with the reproductive organs. Injuries to the penis.
1.
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 by the stallion handler, 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 light in the day.
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 also.
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 it to 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 that will cause a temporary infertility 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 (compared to normal semen parameters)
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 that 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 mares
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 % - 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 that 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.