The Horse

DEC 2017

The Horse:Your Guide To Equine Health Care provides monthly equine health care information to horse owners, breeders, veterinarians, barn/farm managers, trainer/riding instructors, and others involved in the hands-on care of the horse.

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38 TheHorse.com THE HORSE December 2017 7 Hot Weather A severe and prolonged summer heat wave can also impact fertility. "In some states like Texas where heat and humidity are high, this environmen- tal stress can induce a change in semen quality," says Varner. "Some stallions, when exposed to hot weather conditions, start to develop what we call a hydrocele, which is serous fluid accumulation in the cavity that separates the testes from the scrotum. If there is a lot of fluid in there, it tends to insulate the testes and they cannot thermoregulate properly, and semen quality will deteriorate." The best testicle temperature for sperm to remain viable is a few degrees lower than body temperature. 8 Season Annual changes typically don't af- fect stallions the way they do mares. "We recently published an article that looked at the effects of dual hemisphere breeding on fertility of Thoroughbred stallions," says Varner. "In this study we found no ill effects when stallions were used sequen- tially in both hemispheres (going back and forth between summer and winter), when examining 10 consecutive breeding seasons. In this instance stallions tend to be continually exposed to periods of increasing day length, with reduced expo- sure to short winter days." Sperm numbers, however, can decline when stallions are breeding during the shorter days of the year. "With shorter days there is a decrease in testosterone, and sperm numbers go down, and behavior becomes more subdued, whereas with longer days in the spring, everything gets better for opti- mum reproduction," says Squires. Sheerin adds that "the semen won't go from good to bad. It might go from excellent to good, but the stallion will still be fertile. This allows us to do things like collect and freeze semen in the fall, when the main breeding season (and demand for semen) is past." Thoroughbreds can only be bred by live cover, due to registry requirements, so for that breed managers and veterinarians must make do during the U.S. breeding season, which begins in February. 9 Medication "We don't know what kind of effect all medications might have on testicular function, but a person needs to realize that any medication given to a horse could potentially have a deleterious effect on semen quality," says Varner. "If you check the literature, you'll see that drugs like anti-ulcer medications can have a detrimental effect on testicular function." Each stallion also responds to each medication differently. 10 Hormones Some breeders inject lackluster stallions with testosterone for a libido boost. "One or two injections are prob- ably not going to hurt, but if you do this routinely there will be detrimental effects," Squires says. "If a stallion is injected for many days with high levels of testosterone, this can cause a drop in semen quality and also decrease the size of testicles. This can dramatically affect semen quality and sperm numbers." Varner suggests monitoring blood tes- tosterone levels closely in these situations to minimize side effects. Some trainers medicate performance stallions with steroidal hormones called progestogens (e.g., Regumate or altreno- gest) to reduce aggressive male behavior or to make stallions more manageable when showing. "If given for a short period of time, like one month, studies we've conducted have indicated that in mature horses such drugs do not seem to have a detrimental effect on semen quality," says Varner. "Other studies have demonstrated that if the same drug is given in the peripubertal period (when the young horse is reaching puberty), it could have a detrimental ef- fect on semen quality, and the possibility exists that the effect could be long-lasting. "We've examined stallions here that have been treated daily with oral altreno- gest as performance horses over a three- or four-year period, beginning when they were as young as long yearlings or 2-year- olds in training, and they have reduced sperm quality and reduced testicular size," he adds. Dexamethasone and other corticoste- roids can also be detrimental if given for long periods, says Squires. Owners planning to use a stallion for breeding purposes should avoid administering these drugs long-term. 11 Stress Any prolonged stress—be it from hard work, showing, illness, housing, If using an artificial vagina, make sure it's lubri- cated properly and isn't too warm or too cold. ISABELLE ARNON Subpar Semen? During artificial insemination, improper collection techniques can impact sperm quality and motility, which is being analyzed here. STEPHANIE L. CHURCH/THE HORSE

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