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.

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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.

QUIZ:

Please answer the following questions and send the answers to Dr. Sales at jsales@horsecoursesonline.com

Be sure to include your full name, lesson number and email address on all work.

1. Describe what you would expect a veterinarian to do and what tests you would expect a veterinarian to perform if you request a fertility exam on a 4-year-old potential breeding stallion that has never been bred.

2. Name at least 3 physical causes of infertility in the stallion and at least 3 medication or disease related possible causes of stallion infertility.

3. List at least 10 parameters that are measured when performing a semen evaluation and a range of the normal measurement of each of those parameters. (if this has been completed in question one, it does not have to be repeated).

4. Discuss the following terms as they might apply to a potential breeding stallion.

A. Infertility

B. Sub-fertility

C. Impotency

D. Sterility

E. Libido