Shed Ready? Breeding Soundness Exam
Although they are of equal importance, we will begin with the breeding soundness examination of the mare. After all, there are more mare owners in the horse world than stallion owners.
Why, one might ask, is it so important to have a mare undergo a breeding soundness examination? Why not just breed her and hope for the best?
One very strong reason for a breeding soundness examination involves economics. In some parts of the country—Kentucky, for example—it can cost $4,000 to $5,000 per year to maintain a broodmare. If that broodmare yields zero return in a given year, that is $4,000 to $5,000 down the proverbial drain.
Then, there is the matter of properly utilizing stallion power. It is a waste of the stallion’s energy and semen if he is breeding a mare or mares which are unable to conceive. That breeding power could be better utilized on healthy mares capable of conception and maintaining pregnancy.
Time is a factor. Most owners decide when they want the foal to be born and plan the breeding accordingly. If a mare is bred several times and doesn’t become pregnant because of reproductive problems that would have shown up during a breeding soundness examination, that valuable window of opportunity is lost. There also is the matter of the frustration and wasted time involved in teasing a mare and breeding her, all to no avail.
All in all, a breeding soundness examination is practical and makes economic sense.
Of course, if the examination reveals that the mare is unlikely to conceive, the owner faces other problems and decisions. Should she be sold for some other purpose? Should efforts be made to solve her physical problems and convert her from infertility into a breedable animal? It is at that point the horse owner and veterinarian should become involved in a deep and honest discussion concerning prognosis, cost of treatment, and whether, in the case of some old or injured mares, treatment and breeding are the humane things to do.
Again, economics can rear its head. If the mare is just a backyard pet that the owner decided should produce a foal, the decision is pretty simple. If a breeding soundness examination reveals that she is unlikely to become pregnant, she can just go on being a backyard pet.
However, if the animal is a very expensive broodmare with a sterling pedigree, the approach might be totally different. The owner must consider protecting his or her investment. Perhaps it is worth several thousand dollars for a treatment program that has a chance to render her capable of becoming pregnant and carrying a foal to term.
Those are individual decisions to be made by the owner in consultation with a veterinarian. However, it should not take a good deal of discussion or many thought processes to make the decision in favor of a breeding soundness exam, based on the arguments in its favor as listed above.
One of the first considerations for the owner when deciding that a mare should be bred and thus, is a candidate for a breeding soundness examination, involves temperament. This often is overlooked by the horse owner, but it shouldn’t be. Research indicates that highly strung and nervous mares suffer from higher abortion rates due to their higher stress levels which, in turn, elevate cortisol levels that can disrupt the normal reproductive endocrine control mechanisms.
There also is the practical aspect that involves ease of handling. The aggressive, nervous mare might be difficult to breed artificially, for example, or could become overly agitated when approached by the stallion. That type of mare might be one which will lash out at a stallion as he is in the vulnerable position of mounting her.
Temperament carries a step further. It is a heritable trait. Thus, a high-strung, nervous dam and/or sire is apt to produce offspring with the same temperament. In addition, foals often mirror the attitudes and actions of their dams. Thus, it is something of double jeopardy—heredity and environment combining in a negative way.
We mentioned earlier that a reproductive history should be the starting point for the veterinarian. The owner should not want the veterinarian to play guessing games. The practitioner should be provided with everything the owner knows about the mare’s reproductive background.
Included should be information on when she last foaled, how many times she was serviced before she became pregnant, a complete report on her last foaling as to whether dystocia (difficult birth) was involved or whether it was a normal presentation, a rundown on any physical problems she might have had in the past months and even years, a report on her dietary needs and whether there have been changes in her weight in recent months while on a routine diet, her vaccination schedule, her deworming schedule…the list goes on.
In short, the owner should give the veterinarian a running start from an information standpoint in the evaluation of the mare’s breeding capability. While the information might not of itself tell the veterinarian whether the mare is sound for breeding, it likely will help him understand problems that could show up during the breeding soundness examination.
Often of key importance is the age of the mare. Scott Bennett, DVM, of Simpsonville, Ky., who operates Equine Services, a veterinary clinic and hospital that specializes in dealing with problem mares, estimates that in the older mare population, between 20% and 25% are problem breeders. This compares to 2% to 3% for young, maiden mares.
The reason the percentage is higher for older mares is obvious, says Bennett. The wear and tear of multiple pregnancies has had an eroding effect on the reproductive system. Scar tissue forms in the uterus, making it more difficult to harbor and nourish a growing fetus. Sometimes in older mares the oviducts become blocked, preventing the egg from reaching the uterus.
In some mares—including the young, but more often the old—the damage is done before ovulation. Sometimes the oocyte is defective or becomes so during the maturation process within the follicle. When that is the case, infertility is going to result even if every other part of the mare’s reproductive apparatus is in good order.
While reproductive problems proliferate in older mares, they also are present in mares which are bred at an early age. Female equines normally reach puberty between 18 and 24 months of age. Therefore, it is possible to impregnate a young filly only 11⁄2 years old. However, while this is possible, it rarely is advisable. Research has shown that mares bred at that early age are apt to have problems becoming pregnant as well as maintaining a pregnancy. In addition, even if they do become pregnant and maintain the pregnancy, there might be nutritional problems unless the young mare’s diet is monitored closely. A mare of that age is still growing and developing and must have adequate nourishment for her own body as well as for the fetus.
Mares in wild bands in this young age category often become pregnant, and casual observation indicates that it takes a heavy toll. After carrying the foal to term, perhaps at great expense to the mare’s own body, she then must deliver the fetus through what might be a small birth canal and, once that is accomplished—if indeed it is—she must provide sufficient milk for the newborn. Often these young mares are thin and in poor health. The good news for them is that they often do not conceive immediately after the foal is born or even weaned, thus giving their bodies an opportunity to recuperate.
Once the veterinarian has the mare’s history in hand, the next step will be a visual examination of the mare. One of the first things the practitioner will note is the mare’s physical condition. Body conditions often are rated on a score of zero to 10, with zero being emaciated and 10 being obese. In preparation for breeding, one likely would be shooting for a score in the range of 5 or 6. Mares which are obese often have difficulty conceiving, as would be true of mares which were emaciated. Somewhere in between is the correct balance.
Bennett sees more problem with the overweight mare than with one that is slightly underweight. "I’d rather see them (at time of breeding) on the thin side rather than too fat," he says.
The external evaluation also can provide clues concerning whether the mare is a prime candidate for infection of the reproductive tract. For example, the mare with a high tailset and high croup as often seen in Saddlebreds and some lines of Arabians is providing a tipoff that she could be prone to bacterial invasions of the reproductive tract as fecal material falls against her vagina each time she defecates.
This, of course, is not a totally compromising situation. A Caslick’s procedure can be performed to close all of the vagina except for an opening to allow for the passage of urine.
The external examination also will reveal whether the mare is a wind sucker (pneumovagina). Wind-sucking occurs when the vulvar labia becomes weakened and does not function properly by providing a tight outer seal for the reproductive tract. When that occurs, air is drawn into the tract, inflating the vaginal vault.
Mares which suffer from pneumovagina also are prime candidates for urine pooling, which can compromise their ability to become pregnant and maintain a pregnancy. When air inflates the vaginal vault, the entire tract becomes relaxed, eliminating normal barriers against urine pooling within the tract.
Under normal circumstances, urine is evacuated from the bladder into the vulvar vestibule and out the open vulvar labia or lips. However, if the normal slope of the vulva is altered approximately 10 degrees from horizontal or the genitourinary tract slopes forward and downward, a splashback of urine can occur. This means some urine refluxes back toward the cervix and uterus instead of out of the vulva.
Again, age often is implicated. One of the reasons that barriers against urine pooling are no longer functioning, says Gayle Trotter, DVM, MS, Dipl. ACVS, of Colorado State University, is because bad conformation has developed, often as a result of multiple births. The loss of muscle tone allows the vagina to tilt forward and one of the barriers, the sphincter, is unable to provide a tight seal in the tract.
Often, Trotter says, urine pooling mares can be managed successfully by manually evacuating the urine, then breeding them. When a pregnancy occurs, the mare’s hormonal changes will cause the reproductive tract to return to its normal, firmed up state and make the cervix seal tightly.
There are, of course, varying degrees of seriousness to the urine pooling problem. Some mares, for example, are urine poolers only during estrus, while others suffer from the problem on a continuous basis and might require a surgical remedy.
Whatever the case, the fact remains that a mare which suffers from urine pooling could be a problem breeder.
Once the veterinarian has been apprised of the mare’s reproductive history and has conducted a visual external examination, it is time to check out the internal reproductive tract.
The Inner Mare
For this effort, the endoscope and speculum often are the tools of choice for the examiner. The speculum has a more limited use, being utilized primarily to assess the inner membranes of the vagina and the cervix. Basically, the speculum is a hollow tube with a light source attached or through which a penlight can be shined. Sterilized and well-lubricated, it is inserted into the mare’s vagina. The light source then is used to illuminate the mucous membranes lining the vagina and help the veterinarian see the cervix.
The cervix is one of the most important keys involving pregnancy maintenance. It undergoes several changes during estrus, diestrus, and when pregnancy occurs. Once pregnancy occurs, the cervix takes on the role of seal. Its job is to seal off the uterus so tightly that no harmful bacteria can invade and attack the fetus or the uterine membranes.
During estrus, the cervix is fairly relaxed and its tone flaccid. When the mare goes out of heat, the cervical tone increases and the seal becomes tighter. At this stage, the cervix changes color from pink to white. During pregnancy, the cervix is again tightly sealed and becomes white in color, with a mucous plug acting to enhance the effectiveness of the seal.
The next step in the breeding soundness examination might involve rectal palpation. The skilled examiner can check the condition of the cervix and assess the tone, size, and texture of the uterus, uterine horns, fallopian tubes, and ovaries through the relatively thin lining between the rectum and the reproductive tract. The practitioner will be able to determine, among other things, whether there are structural abnormalities during palpation.
One of the tools often used in breeding soundness examinations of mares is ultrasound. Endometrial cysts, fibrous masses, fluid, uterine tumors, ovarian tumors, ovarian hematomas, and ovarian cysts often can be identified using ultrasound.
A problem that might show up during rectal palpation and ultrasound is uterine cysts. Repeated bouts with endometritis (infection in the uterus) can result in uterine cysts, says Bennett. Cysts are rare in young mares, he said, but often develop in an older mare after multiple births and can provide a limiting factor in the mare becoming pregnant and carrying a foal to term.
The cyst problem crops up in the wake of scar tissue that develops as the result of infection or multiple births. What happens then is a clogging of the lymphatic draining system by scar tissue. The result is a cyst or cysts filled with fluid that normally would be evacuated.
"A few cysts within the uterus won’t make that much difference unless they are large," says Bennett. "Their ability to compromise the functioning of the uterus is dependent both on their size and number. Normally, I don’t worry about two or three small cysts, but one big cyst can become a major problem.
"In some mares, there will be 10 or 12 cysts, and their presence in that number will definitely cause problems even though they may not be large. The cysts become physically obstructive, sometimes preventing semen from entering the uterus, and, if a pregnancy does occur, can compromise mobility of the embryo. That is how the embryo codes—giving the signal that a pregnancy has occurred—by wandering through the uterus for the first 18 days."
If the examiner finds indications that there might be cyst problems within the uterus, a more thorough examination is called for. Following are some of the approaches taken to provide the veterinarian with a more thorough knowledge of what is going on within the uterus.
Endometrial Culture—An endometrial culture is a general evaluation of the bacterial status of the uterine lumen. "It must be remembered," says Bennett, "that a negative culture simply means you did not culture any bacterial growth from that swab." Conversely, a positive culture does not necessarily mean that the entire uterus is filled with infectious agents. However, it will tell the practitioner and owner that the mare will likely have to be treated before she can be bred.
Cytology—This involves studying cell samples under the microscope.
Endometrial Biopsy—In this procedure, small samples of uterine tissue are retrieved and studied.
Hysteroscopy—Hysteroscopy involves using a flexible fiberoptiscope to visualize the structures within the uterus. Bennett explains the utilization of hysteroscopy this way: The mare’s rectum is manually emptied of manure. The uterus then is filled with filtered air, carbon dioxide, or fluid. Bennett says his preference is either filtered air or carbon dioxide because fluid often will cloud with pus if endometritis is present, making the exam more complicated. The structures that can be examined with the fiberoptiscope include the cervix, endometrium, and tubal-uterine junctions. Abnormalities that Bennett says can be seen easily via the fiberoptiscope include infection, cysts, scar tissue, adhesions, and tubal-uterine junction problems.
Laparoscopy—This involves a surgical procedure, most often performed through the flank, in an effort to view parts of the reproductive tract. It is not used frequently anymore because of the advent of ultrasonography.
Tubal Patency—Bennett believes that a blockage of the oviducts cannot be diagnosed through palpation, ultrasound, or laproscopic examination unless a grossly obvious condition exists. The tubal patency procedure, simply put, involves flushing a die through the oviduct and, by observing what occurs, determining where the problem lies if indeed there is a problem.
As mentioned earlier, when an abnormality shows up during a breeding soundness examination, the owner must, in consultation with the veterinarian, determine what procedures, if any, should be taken.
Medical advances have helped make that decision in some cases. If a mare is suffering from uterine cysts that threaten her ability to get pregnant and maintain pregnancy, for example, laser surgery is an option.
"The laser has been absolutely a godsend," says Bennett. "A lot of the uterine cysts are high up in the horn, and you literally have to go around a corner to get to them. That is difficult to do with a traditional straight instrument."
The modern technique involves placing the laser within an endoscope. The endoscope then is inserted into the uterus via the vagina. This approach allows the practitioner to visualize the interior of the uterus, locate the cysts, and vaporize them.
Once the mare has been thoroughly examined externally and internally, there is still another area to be assessed before she can be declared to be breeding sound—a hormonal evaluation, especially as it pertains to progesterone. A hormonal assessment can be made via a blood test.
To understand the role played by progesterone, we must digress for a moment to discuss what happens when a mare’s hormonal system goes into operation during estrus.
Hormones & Mares
As the mare’s brain records increased light and higher temperatures with the advent of spring and summer, the hypothalamus gland, located within the tissues of the mid-brain, is stimulated. It signals the start of the reproductive system by producing a gonadotropic-releasing hormone (GnRH). When GnRH is secreted in the proper quantity, the pituitary gland, located at the base of the brain, is stimulated. The pituitary then secretes two hormones that affect the ovaries. The first hormone is known as follicle stimulating hormone (FSH). It travels along the bloodstream to the ovaries, where it stimulates development of one or more follicles.
The follicles, when they reach 20 to 25 millimeters in diameter, secrete estrogen. This hormone stimulates estrual activity, causes relaxation of the cervix, stimulates contractions along the mare’s reproductive tract, and signals the pituitary gland to cease secretion of FSH. At the same time, it stimulates release of the second gonadotropic hormone—luteinizing hormone (LH).
The luteinizing hormone facilitates maturation and ovulation of the growing egg-bearing follicle.
Ovulation occurs when the mature egg leaves the follicle and begins its trip through the oviduct. In the wake of ovulation, the estrogen levels fall, and the remains of the ovulated follicle form a corpus luteum (CL) or yellow body. The luteal cells secrete the hormone progesterone. It is the job of progesterone to shut down the estrus-stimulating hormones and to set the stage for maintaining a pregnancy.
Progesterone’s initial task is to subdue the actively contracting reproductive tract and to tighten and close the relaxed and open cervix. It also prohibits the secretion of FSH and LH from the pituitary, thus effectively putting the mare out of heat. When the proper amount of progesterone is produced, all of the above happen in proper order. However, not all mares secrete the correct amount of progesterone.
When that is the case, the other hormones swing into action to terminate the pregnancy and bring the mare back into heat.
Fortunately, progesterone levels can be monitored and supplemental progesterone can be administered. However, if a progesterone dysfunction is not detected early, the mare can go through a number of estrous cycles without a viable pregnancy and in the process perhaps miss the window of opportunity for reproduction that year.
Proper timing of secretion, and proper levels of all hormones, are required to maintain a reproductive balance during breeding and pregnancy. When there is an imbalance anywhere along the way, fertility problems follow. Mares which are sub-fertile because of an imbalance must be monitored and dealt with by a veterinarian. However, before imbalances can be dealt with, they must be discovered. A breeding soundness examination can pinpoint the problem if there is one.
A routine breeding soundness examination will not necessarily bring to light every reproductive problem that might afflict an individual broodmare. However, having such an examination is a wise and sound investment because it will reveal the majority of the problems.
It should be noted that differences of opinion exist among veterinarians who work with broodmares. There can be multiple concepts and multiple approaches to the management of the same problem. In short, there might be more than one way to achieve the same result, which is pregnancy and production of a foal.
For help in the discussion on a stallion’s breeding soundness examination, we turn to Dickson Varner, DVM, MS, Dipl. ACT, and Terry Blanchard, DVM, MS, Dipl. ACT, both of Texas A&M University. The pair published a series of in-depth papers involving examination of stallions for breeding soundness. Varner also was one of the speakers on the subject at last year’s Stallion Reproduction Symposium conducted by The Society For Theriogenology in Baltimore.
"The primary objective of a breeding soundness examination," Varner and Blanchard wrote in one of their reports, "is to determine whether a stallion has the ability, under the circumstances in which it will be used, to successfully intromit the penis into an artificial vagina or the vagina of a mare and ejaculate semen of sufficient quality to achieve an acceptable pregnancy rate when bred to a reasonable number of fertile mares in a breeding season."
As already mentioned with mares, the first step in the breeding soundness examination is to gather the stallion’s history, especially as it relates to reproduction.
The history, Varner and Blanchard say, should include the lineage of the stallion, vaccination and deworming dates, feeding and exercise program, past and present usage, previous breeding performance, results of any previous breeding soundness examinations, and dates and types of previous illnesses, genital infections, or injuries as well as types of treatment given.
Explicit information about previous and current reproductive management, they explain, can be informative, particularly if a recent change in management has been associated with a change in fertility status.
They go on to say that it often is helpful to obtain specific information about recent breeding performance, which would include the following.
For horses bred by natural service:
Number of mares bred and number pregnant.
Frequency of breeding. This should include the number of mares bred daily as well as in the previous week.
Number of services per cycle.
Pregnancy rate per cycle.
Cumulative pregnancy rate for season.
Pertinent information about mares, including the number of maiden, lactating, and barren mares bred, and respective pregnancy rates for each group.
Sexual behavior. Does the stallion fully insert the penis into the vagina, remain mounted until ejaculation occurs, and show positive evidence of ejaculation (i.e., sperm present in dismount sample) during copulation?
For horses bred artificially, all of the first six items would apply, plus the following:
The number of mares bred with each ejaculate as well as the frequency of collection.
Average volume, concentration, total sperm number, sperm motility, and sperm morphology in ejaculates collected.
Type and source of semen extender used. This can include the water source and type and source of antibiotic added to the extender.
Semen handling and insemination protocol. This should include the type of artificial vagina used and its maintenance as well as the type of lubricant used.
Interval from semen collection to breeding and method and storage for semen held for later insemination.
Pregnancy rates for other stallions bred under the same management scheme and using the same semen extender and handling methods.
Next, comes an assessment of the stallion’s general body condition and health. Varner and Blanchard have this to say to fellow veterinarians who are conducting stallion breeding soundness examinations:
"Note any conformational traits or chronic injuries, such as lamenesses, that might affect the ability of the stallion to withstand a vigorous breeding season. Pay particular attention to the eyes and limbs. While horses with eyesight problems can be used for breeding, special housing and management considerations may be required for the safety of the stallion and handlers.
"Chronic hindlimb lamenesses or back injuries that might at first appear to be mild can worsen with age or during an intensive breeding schedule.
"Poor teeth condition can adversely affect the stallion’s ability to maintain body condition, particularly if the horse is pasture-bred. Also note any evidence of recent or current infectious disease, because a rise in body temperature can adversely affect spermatogenesis. Poor sperm quality may be evident as early as five to seven days after the rise in body temperature, but the most dramatic effects are likely to be seen about 30 days later.
"Additional laboratory tests, including serologic testing for equine infectious anemia or equine viral arteritis, a complete blood count (CBC), a serum chemistry profile, fecal egg counts, and urinalysis sometimes are performed. In some cases, blood typing is requested.
"Finally, do not overlook evidence of potentially heritable conditions (such as cryptorchidism, parrot mouth, wobbler syndrome, and microthalmia or tiny eyes). Warn the owners of stallions with such conditions that these undesirable traits might be transmitted to offspring."
As is the case with mares, the age of the stallion can have a bearing on his breeding soundness. Stallions reach puberty sometime between 12 and 24 months of age, but do not reach sexual maturity until about age five. Puberty has been defined in practical terms as the age at which a young stallion’s ejaculate first contains 50 million spermatozoa, of which 10% are progressively motile (able to move in a straight line or forward direction).
Generally speaking, the very young and the very old stallions would be less apt to be as "breeding sound" as a healthy stallion which had reached sexual maturity at age five.
Libido plays a large role in determining the number of mares a stallion can service during a breeding season and is an important consideration in a breeding soundness examination. Juan Samper, DVM, MSc, PhD, a private practitioner in British Columbia who specializes in equine reproduction, addressed this issue during the Baltimore Theriogenology symposium.
"Libido, which is thought to be a genetically acquired trait, can be modified by handling and environmental conditions, such as housing," Samper said. "Therefore, testosterone levels and libido can be altered by interaction between stallions and mares and with exercise. Many times, poor libido is a limiting factor in the number of mares a stallion can cover. The number of covers a stallion can make in a day varies with the individual stallion. Factors such as age, physical abnormalities, and testosterone levels play an important role. There are some stallions that can breed two or three times a day, seven days a week, and some that can only cover one mare per day.
"The length of the breeding season also plays a role in the number of mares that can be mated. The Thoroughbred season is generally from Feb. 15 to July 15. Therefore, the number of mares that can be presented during this time is somewhat limited in a natural breeding program. In warmblood stallions, an excess of 350 mares can be bred with every-other-day collection and with stallions of average semen quality."
Varner, in his talk during the symposium, also underlined the importance of libido in a breeding stallion and he, too, emphasized that it is an important aspect of a breeding soundness examination.
Excellent semen quality in a breeding prospect, he said, is inconsequential unless the stallion also has the desire and ability to deliver the semen to the mare’s reproductive tract or an artificial vagina.
"Sexual behavior can only be analyzed by bringing the stallion in contact with a mare in estrus," he said. "Typically, a stallion with good libido shows immediate and intense desire for the mare, manifested by restlessness, pawing, vocalization, intimate precopulatory activity, such as sniffing, licking, and nipping the mare, exhibition of the ‘Flehmen’ reaction (curling the upper lip, primarily in response to sniffing of the mare’s genitalia or urine) and development of an erection.
"The ability of a stallion to copulate normally (develop an erection, mount without hesitation, insert the penis, perform intravaginal thrusts, and ejaculate) should be assessed properly before the stallion is considered a satisfactory breeding prospect."
Checking the stallion’s libido can dovetail with the beginning phases of the genital examination. Varner and Blanchard recommend that the penis and prepuce (a fold of skin or foreskin that covers the penis) be examined after the stallion is teased to erection and before semen is collected.
The skin of the prepuce, they say, should be thin and pliable, with no evidence of inflammatory or proliferative lesions. Common penile and preputial lesions, they state, include those of traumatic origin, such as lacerations, hematomas, and, rarely, cicatricial scar formation (scar tissue formed in the healing of a wound).
The penis itself might have to be cleansed before it can be properly examined and evaluated, due to the possibility of smegma that develops from epithelial debris mixed with gland secretions. Although rare, the two researchers say, smegma buildup can lead to bacterial infection, which can irritate the penis and cause the stallion to be reluctant to breed.
After the prepuce and penis are checked thoroughly, the examiner likely will turn his attention to the scrotum. "The stallion’s scrotum should be thin and elastic, with a distinct neck," Varner and Blanchard say. "The scrotum and its contents are normally pendulous (except during cold weather), but may be drawn toward the body during palpation because of voluntary contractions of the cremaster muscles. Both testes and their attached epididymides should be freely movable within their scrotal pouches."
Both testes should be oval, with a smooth, regular outline and a slightly turgid, resilient texture, the two researchers say. The position of each testis within the scrotum can be determined accurately by palpating the attached epididymis (the long cordlike structure along each testis where spermatozoa are stored).
Also evaluated is the spermatic cord. Spermatic cords, say Varner and Blanchard, should be of equal size and uniform diameter (2 to 3 centimeters). The spermatic cords descend down through the abdominal opening and attach to the testes.
An important determination to be made in regard to the testicles during a breeding soundness examination is testicular size. Research has shown that testicular size correlates highly with daily sperm production. Thus, accurate testicular measurements can help predict the number of mares a stallion can breed.
Once the external examination of genitalia has been completed, the veterinarian likely will want to do an examination of internal genitalia.
Varner strongly recommends that, if possible, stallions should be placed in stocks for this examination to negate the possibility of injury to the horse and the human doing the examining. At the Baltimore symposium, he gave this description of the examination:
"The hand should be well lubricated and all manure in the rectum and distal colon removed before evaluation of pelvic and abdominal structures is attempted. The two vaginal rings (abdominal orifices of the inguinal canals) are palpable as slit-like openings ventrolateral to the pelvic brim. The deferent duct and pulse of the testicular artery often can be detected at the opening. The site is evaluated for size as well as for evidence of adhesions or herniation of viscera. The diameter of the opening is normally 2 to 3 centimeters. A larger opening may predispose the stallion to inguinal herniation. Some of the accessory genital organs also can be detected by palpation per rectum.
"Transrectal ultrasonography is occasionally used for evaluating the internal reproductive tracts of stallions. This approach can be used to locate and assess the accessory genital glands (such as the paired vesicular glands, bulbourethral glands and ampullae, and the prostrate gland), pelvic urethra, vaginal rings, and (in the case of cryptorchids) intra-abdominal testes."
Also a part of most stallion breeding soundness examinations is testing for venereal diseases. In most cases, a culture is obtained by utilization of a swab in the urethra. Infected stallions, it almost goes without saying, would not pass a breeding soundness examination.
If the stallion breeding prospect passes all of the external and internal examination hurdles, and proves to be free of venereal disease, there still is one major test that awaits—an evaluation of sperm quantity and quality.
"Total sperm number, calculated as the product of sperm concentration and semen volume, is one of the more important measurements used in estimating a stallion’s fertility," report Varner and Blanchard. "Total sperm number in an ejaculate is subject to seasonal variation, but is also affected by numerous other factors, including frequency of ejaculation, age, testicular size, size of extragonadal sperm reserves, and various forms of reproductive disease.
"Total number of sperm in stallion ejaculates typically ranges from three billion to 20 billion. When the stallion is young and on a frequent breeding schedule, sperm numbers are usually at the lower end of this range. Sperm numbers are usually at the upper end of this range when the stallion is older and on an infrequent breeding schedule. Fertile stallions should be expected to have at least four billion total sperm in the first ejaculate and two billion total sperm in the second ejaculate after one week of sexual rest."
The examining veterinarian might want to check sperm motility and morphology. Motility refers to an assessment of spontaneous movement of sperm, while morphology deals with the general health of the sperm.
Just how much weight should be placed on these two aspects of the breeding soundness exam appears to be somewhat debatable. It seems generally agreed that the best of all worlds would be to have sperm in great numbers that are progressively motile and all in good health. However, research has shown that a number of stallions with sperm that appear to be lacking in optimum motility still are able to impregnate mares.
Varner and Blanchard have this to say:
"Spermatozoal motility reflects the viability of a sperm population. A positive relationship between sperm motility and fertilizing capacity has been demonstrated in many species, although this correlation cannot be considered absolute. In a recent study of semen and sperm motion characteristics involving 99 stallion seasons, the characteristics with the highest correlations to fertility were the percentage of motile and progressively motile sperm; yet, only 20% of the variation in fertility among the stallions studied was due to differences in sperm motility."
Much the same has been found with sperm morphology. There have been stallions whose ejaculates contained more damaged sperm than desired, but the horse still is a good breeder.
It could be, say researchers, that the number of normal sperm is of more importance than the number of abnormal sperm because the abnormal sperm do not seem to have a detrimental effect on normal sperm.
Even if a stallion passes a breeding soundness examination with flying colors, it does not mean that he will impregnate every mare put to him. There are numerous other factors involved. For example, a stallion which has a book of healthy, young, maiden mares likely would be much more successful than a stallion which has a book of older mares with reproductive problems.
Management of the stallion also has a strong influence. If a stallion is covering mares two or three times a day via live cover, his success ratio might be lower than the stallion which is collected once every other day for artificial insemination.
There are other aspects of management that can have an influence, such as exercise and nutrition. Stallions need to be well fed, but obese stallions, even though they have passed a breeding soundness examination, might not have the libido of the stallion which is not carrying as much weight.
Horses of either sex are, by nature, free-roaming, grazing animals. This means that the breeding stallion should have plenty of exercise on a daily basis if one expects him to remain physically fit and capable of covering his particular book of mares.Starting a reproductive program with a breeding soundness examination, then following it with good management, is the best insurance available for a successful breeding season.
About the Author
Les Sellnow is a free-lance writer based near Riverton, Wyo. He specializes in articles on equine research, and operates a ranch where he raises horses and livestock. He has authored several fiction and non-fiction books, including Understanding Equine Lameness and Understanding The Young Horse, published by Eclipse Press and available at www.exclusivelyequine.com or by calling 800/582-5604.