Page 117 - January 2021

EQUINE HEALTH
WHEN TO DO IT
Sometimes people wait to geld a crypt- orchid, trying to give him time for the undescended testicle to come down, if it
will. A few colts have temporarily retained testes that are caught in the inguinal canal below the abdomen. This occurs most often in ponies, however. The pony colt may have one small testicle that does not descend when the normal one does. The smaller one may eventually grow larger and descend into the scrotum by the time the animal is two or three years old.
If you check a young horse and cannot feel the testicles, the question is often asked regarding how long you should wait before you determine that the colt is truly a cryptor- chid. Tibary says the testicles should both be there at birth, or no later than the first month after birth. “However, there are reports of some stallions being two years old before the testicles descend,” he says.
If a testicle is caught partway up the inguinal canal, there is a chance it will come down when the horse matures. Enlargement brought about by puberty and increased weight of the testicle helps pull it down. But body heat in the flank may inhibit proper growth of the testicle and it may not enlarge and descend.
“Once it’s been determined that a colt is a cryptorchid, we generally recommend that the retained testicle be removed by the time he is about 12 months old. If the horse is still a high flanker or abdominal cryptorchid, it’s time to do something about it.” Tibary recommends checking colts during their first month of life to see if everything is normal.
Yarbrough says that if the testicle has not descended through the internal inguinal ring by the time the ring starts to contract at about 6 months of age or earlier, it will not get out and will be permanently trapped in the abdo- men. “It’s possible for a high flanker to have
a testicle not make it all the way down to the scrotum until 2 years of age, but very unusual. If you know the colt is a cryptorchid and you want to geld him while he is young (as a foal or weanling) there is no advantage to waiting. It’s actually easier to do an inguinal approach on foals because they have less inguinal fat and the blood vessels are smaller, so the explo- ration is easier,” he says.
SHOULD A CRYPTORCHID BE KEPT AS A STALLION?
Keeping a cyrptorchid as a breeding stallion is controversial, and most horsemen and veteri- narians advise against it. There is a genetic com- ponent to this problem, and offspring may have a greater chance of having the same problem. Some breeds allow cryptorchids as stallions and others don’t. Most horsemen don’t want to per- petuate the problem; cryptorchid colts are more difficult and expensive to geld, and a cryptorchid stallion is at a disadvantage for breeding. He will still be fertile with only one testicle, but can’t produce as many total sperm as he would with two testicles and won’t be able to breed as many mares. If anything happens to his one functional testicle, he is out of business as a sire.
“For a testicle to develop and function normally, it must be able to thermoregulate.
It needs to be at a temperature a little below normal body temperature. That’s why the cremaster muscle will draw the testicle up
or down, depending upon whether ambient temperature is warm or cold. A testicle retained within the abdomen will not produce viable sperm and cannot function normally. A testicle in the flank will also be at risk for reduced sperm count and viability,” says Yarbrough.
This genetic defect is not as harmful to the horse as some other inherited faults, since the affected animal can live and function nor- mally but may have aggressive behavior which could put handlers at risk. “We castrate a high percent of these animals, and as long as horse owners don’t mind the added expense to geld the progeny of a cryptorchid stallion, cryptor- chidism may be an acceptable inconvenience
if the horse has other qualities that are desired. It’s a matter of whether the horse owner wants to put up with the inconvenience, and whether we want to take on a bigger financial burden when gelding the offspring,” he says.
Tibary says leaving a horse a cryptorchid can be dangerous for handling him. “Some people say that cryptorchid stallions can become a lot more dangerous than normal stal- lions, and I have seen this in Thoroughbreds. The crankiest Thoroughbreds I have seen were cryptorchids. Their behavior is altered by the testicle that is not normal,” he says. If a tumor develops in that testicle, it can also change the horse’s behavior by altering the hormone bal- ance, triggering a change in personality.
Tibary says he has seen a lot of cryptorchids in Akhal-Teke horses because it is a breed of small numbers with a limited gene pool.
INCIDENCE AND HERITABILITY
Cryptorchidism occurs in most mammals, perhaps more often in domestic animals than in wild ones. We have bred horses selectively for traits that suit our purposes and sometimes in our efforts to choose breeding stock with characteristics we desire, we overlook others. Thus, we may perpetuate or increase the inci- dence of certain problems.
Cryptorchidism in horses is thought to be inherited, though the actual mechanism of inheritance is not yet fully understood. Tibary says it has been confirmed in sheep and swine
to be hereditary, and we assume it is in horses. “Some authors think it’s inherited as a dominant autosomal (in a pair of chromosomes) and others think it’s a recessive gene (that must be inherited from both parents to show up in the offspring). In my experience, I’ve seen a lot of cryptorchids in Akhal-Teke horses, a breed of small numbers with a limited gene pool.”
Within all breeds there are some bloodlines that produce a greater number of cryptorchids than the average for that breed, and some breeds have a higher incidence. A study that looked at more than 5,000 cryptorchid horses found the highest number in Percherons, Quarter Horses, Saddlebreds and ponies, says Tibary.
“From that study, it was also found that the breeds that don’t have many cryptorchids are the ones that have tried to eliminate this trait by not allowing them to be used for breeding.” This lends credence to the idea that it is inherited.
“In that study, it was also found that the left testicle is more commonly retained than the right, in horses that are abdominal cryptorchids. One speculation as to why this occurs is because of the way the kidneys are placed. One kidney is higher than the other. So, it has to do with position of the kidneys and testicles while the fetus is developing,” says Tibary. Sometimes both testicles are retained in the abdomen (bilateral cryptorchidism) but this is rare. More often, just one is retained.
Once it’s been determined that a colt is a cryptorchid, we generally recommend that the retained testicle be removed by the time he is about 12 months old.
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