As a veterinarian, one of the most interesting aspects of the profession is to work with a horse and owner to investigate, detect, and treat a problem. When we are lucky, careful attention to detail will reveal the problem. At other times, we have to ask many questions and perform a battery of diagnostic procedures and tests before are able to help horse and owner. Unfortunately, there are times when a million questions, and numerous tests do not detect or correct the problem.

Veterinarians and physicians are not magicians-but I sometimes think that by not explaining things clearly to our clients we lend too much mystery to our investigations, unwittingly giving false hope which may lead to unrealistic expectations. Much of the mystery and detective work in veterinary medicine is due to the fact that animals don't speak our language. However, as many people who have spent considerable time with animals can verify: if we listen to animals on their terms (not ours), and are patient and observant, they will speak to us in volumes

I wrote this article to shed some light on the thought processes of at least one veterinarian and to also share some of my experiences. I hope it is of some use to you.

Case study 1: A young stallion with decreasing fertility.

A nine year old Quarter Horse stallion was brought to me last year because he was settling (impregnating) fewer mares than the previous breeding season. The farm manager, who was responsible for breeding the horse, was getting worried because ultrasound exams by the regular farm vet indicated that the stallion had not gotten a mare pregnant in about three weeks.

We knew that a semen evaluation would most likely be performed and the first thing to investigate in any semen evaluation is the general health and physical condition of the horse. Nothing out of the ordinary was seen on physical exam; the stallion was in good flesh, eating and drinking normally, and had no observable illness or fever both during the time of the exam or in the previous months. (If a stallion has a systemic infection with a high fever this can lead to a temporary or permanent infertility.) The stallions testicles were of normal shape, size, and firmness, so obvious testicular problems or disease were ruled out. I had never seen the farm, but it was obvious that the very capable farm manager had a special affection for, and was taking very good care of this horse.

The next vital information to examine during a fertility exam is breeding history-, again, the farm manager had done a great job and taken very detailed records on each and every breeding and pregnancy. The stallion bred 28 mares the previous breeding season and had a 92% pregnancy rate. To get this pregnancy rate the stallion bred some mares more than others. When averaged out over all the mares during the entire season, it took two breedings per cycle and 2.3 cycles per pregnancy. These averages are within normal, so at least he was fertile last season. If, on the other hand, it had taken more breedings per cycle and more cycles per pregnancy it would have indicated that too many breedings were necessary for pregnancy. This in turn could have led to the suggestion of infertility (not sterility) the previous season or management inefficiency, namely, not breeding mares at the right time or infections in one or more mares.

The eight mares the stallion bred during the current season were mostly young mares, ranging in age from four to l6 years. If the stallion had bred only older mares (12 years or more)with poor pregnancy rates themselves, then we might have cause to question the fertility of the mares. However, this was not the case-most of the mares had foaled recently or were maidens (never bred, often the most fertile). Nothing in the stallions history or physical exam shed any light on the problem.

The semen evaluation was the next part of the examination. During this part of the exam we look at the sperm's swimming action or, more precisely, motility; morphology (shape); concentration; total numbers of sperm; acidity (pH); and abnormal bacteria. Prior to collecting a stallion, we tease him so that he drops his penis, permitting us to physically examine the penis for any lesions and take a swab for bacterial culture of his urethra. The culture allows us to look for abnormal bacterial growth, but the results take two or more days to acquire.

After the culture was taken, we washed the stallion's penis with warm water (he was clean from regular breeding and did not need soap) and dried him carefully. We collected the stallion's semen with an artificial vagina (AV) while he mounted a "jump mare" in heat. The farm manager handled the stallion and had always allowed the horse to misbehave and charge the jump mare. We did not try to stop this behavior at this point, because we had semen collection as the number one priority and he was not injuring the mare or jeopardizing anyone at the time. Once the stallion mounted the jump mare, he behaved and mated normally. However, as the breeding continued, a significant abnormality was noted; near the end of the collection procedure he appeared uncomfortable, squealed angrily, and backed off the mare.

When a stallion is collected, some (very few considering what we are doing) do not like the feel of an AV, resent it, and stop breeding. Most stallions can be easily trained to the AV, and so we allowed the stallion to mount the jump mare again and proceeded with the collection. He mounted normally and this time we were able to collect him. Again, just before and during ejaculation he made vocalizations of resentment and even though the collection appeared was stallion complete, he definitely frustrated or angry. In fact, the stallion kicked out with both regular legs as he was led away from the jump mare! Fortunately, the mare handler had walked the mare forward and the kick barely made contact.

This type of behavior is unusual, even when an AV is used. However, it was possible that the AV was the source of the problem. Another common reason for a stallion to back off during breeding in this manner is due to the stallion experiencing pain-most commonly in the hock or back.

Unfortunately, kicking can be a common behavior in some stallions. In this case the farm manager assured us that although he allowed the stallion to charge mares, he never kicked at them. Now the farm manager was extremely worried because of the stallion's display of pain and frustration! It was only later that we were able to rule out the above reasons as the source of the stallion's discomfort.

During a semen evaluation the usual procedure is to collect the stallion two times, one hour apart.

This allows us to see if the stallion has normal numbers of sperm and if his sperm storage is normal. The one hour interval also permits us to look at motility, morphology, concentration and so on. The stallion's ejaculate volume was 135 ml, a normal amount of semen. The sperm motility was about 70% progressive (70% of the sperm are strong wigglers and moving in straight paths), also a normal level. The concentration of sperm was 120 million per ml, also well within normal levels. We stained the sperm but did not have time to examine the morphology before it was time for the second collection of the exam.

While looking at motility we noticed many large round cells within the semen. This was an abnormal finding because these cells could be immature sperm or white blood cells. The presence of many immature sperm would mean the stallion is not storing sperm properly, releasing them before they mature enough to fertilize an egg. This alone wouldn't necessarily answer the question of this stallion's infertility, because many stallions with normal fertility have abnormally high numbers of immature sperm. If what we were seeing were white blood cells it would possibly indicate an infection somewhere in the reproductive tract. Finally, we were getting somewhere in our investigation.

When we introduced the stallion to the jump mare again he was very excited and extremely willing to breed. This time we anticipated and stopped his charging. He mounted the mare, and, while positioning himself behind her, appeared to ejaculate onto the mare's flank. Premature ejaculation is an extremely unusual finding and one which wouldn't explain his problems because he had been breeding mares normally. Just to be thorough, we scraped the semen off the mare's side and examined it under a microscope after collecting the stallion for the second time.

The sample from the mare's side gave us one major answer; the fluid under the microscope proved to be all white blood cells with no sperm present! The stallion did not ejaculate prematurely, but discharged pure pus prior to ejaculation! We now knew that an infection of his genital tract was present.

Figure legend: Cross section of the genital tract of a stallion, facing the left. only the right half of the anatomy is shown. 1) testis, 2) epididymus, 3) spermatic cord, 4) vas defrens, 5) ampulla, 6) vesicular gland, 7) prostate, 8) bulbourethral gland, 9) urethra: a) pelvic & b) penile, 10) penis, 11) prepuce, 12) scrotum, 13) bladder. (Adaption from McKinnon, A.O. and Voss, J.L. eds., Equine Reproduction, Lea & Febiger, Philadelphia 1993).

The genital tract includes testes, epididymus, vas defrens, bulbourethral glands, prostate, ampulla, seminal vesicles, urethra, urethral fossa, and penis. Somewhere within this tract an infection was festering. To answer the question of where the infection was localized, we performed an ultrasound exam of the stallion's testes and internal reproductive glands. The testes looked normal but his right seminal vesicle (#6, illustration) appeared slightly enlarged. Now we knew we were hot on the trail.

Next, we performed a urethral endoscopy, placing a small diameter endoscope (a long flexible camera which allows us to look into places inaccessible by any other means) into his urethra. After tranquilizing the stallion, the endoscope was slowly introduced into his urethra at the prepuce (#11, illustration). After inserting the endoscope over two feet through his pelvic urethra (illustration, #9a), we found the source of the infection at the seminal vesicles (#6, illustration). The openings of the seminal vesicles (glands which supply fluid to the ejaculate to increase its volume, among other things) into the urethra were matted with pus (See before treatment photo). We had what we considered a definitive diagnosis of seminal vesiculitis (the suffix "itis" means inflammation).

Seminal vesiculitis is a fairly uncommon disease in stallions. The stallion's pain was apparently originating from the vesicles when they contracted to add their fluid to the ejaculate. It is unknown how he contracted this infection, but venereal transmission from a mare during breeding is exceedingly rare, although possible. A much more common cause of stallion genital tract infection is from over-washing before breeding. The stallion was angry because breeding, which used to be pleasurable, was now painful. We started the stallion on high doses of the powerful broad spectrum antibiotic trimethoprim sulfa (SMZ). SMZ is often an antibiotic of choice for the genital organs because its absorption to some areas of the male reproductive tract is good. When the culture results came back they fortunately showed the bacteria to be sensitive to SMZ and the stallion was treated for two weeks. If the bacteria were resistant we would have been forced to use other antibiotics, even if their absorption is not as good.

When the stallion returned two weeks later, urethral endoscopy revealed that no pus was present at the seminal vesicle openings (See after treatment photo). The stallion continued with his breeding and once again was settling mares-with one improvement, the stallion was no longer allowed to charge mares.

The above case demonstrates how detailed records, careful examination, and some detective work can help in the diagnosis of a problem. Even less involved problems require careful attention to detail. In a future issue, I'll describe a case study of a young mare who was not pregnant after three cycles.

Before treatment:

After treatment: