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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37 December 2017 THE HORSE TheHorse.com are simply due to limited numbers in the breed and the need to propagate the breed by use of subfertile individuals." 2 Genetics Every breed has certain lines known for having low fertility. "There is a line of Standardbred stallions, for in- stance, that have fertility problems," says Sheerin. "You can say the same for Thor- oughbreds and Quarter Horses; there are some family lines that have poor-quality semen." There's usually a genetic reason a stal- lion isn't as fertile as others. "Stallions are a lot like men; we are not culled based on reproductive ability, as would be the case for most livestock," says Varner. Rather, stallions are typically se- lected as sires based on their pedigree, competitive performance record, and conformation. "Little regard is given to their reproduc- tive potential," says Varner. "If a stallion has a great performance record he is generally considered a good candidate for breeding. He may start his breeding ca- reer with reduced fertility and require vet- erinary assistance to maximize fertility." In other domestic livestock species, such as cattle, pigs, goats, and sheep, fertility is a major consideration. Produc- ers do not want to perpetuate animals with low fertility. "In cattle, freezability of semen is also very important, especially in dairy cattle," Varner adds. "Dairy bulls have been screened for decades for freez- ability of semen, but that's not the case with stallions." As a result, stallion semen's freezability is not great and can vary considerably between horses. Testicular size is also genetic, says Squires, adding that size affects semen quantity more than it does quality. 3 Body Condition Stallions with excessive body condition (a score of 7 or higher on the 1-9 Henneke Scale) have more fat in their scrotums, insulating the testicles, than those in moderate condition. "This interferes with proper thermo- regulation, which interferes with semen quality and fertility," says Sheerin. In other words, the testes and the sperm within stay too warm. By the same token, a starving horse or one in poor body con- dition will also have poor semen quality because he's not receiving enough nutri- tion to support reproductive health. 4 Nutrition Extreme dietary changes can affect sperm output and quality, says Squires. Fortunately, most owners he's worked with feed their breeding stallions adequate, well-balanced diets. "If a stallion is eating feed that is high in estrogen, however, this can have an adverse impact on semen, due to the hormonal feedback on the hypothalamic- pituitary axis," says Sheerin. "On the oth- er hand, feeds that are high in omega-3 fatty acids (e.g., fish oils, flaxseed oils, etc.) can have a beneficial effect, aiding the longevity of semen in some cases." Squires adds that offering supplemen- tal omega-3 fatty acids to stallions that have poor semen quality post-cooling or -freezing can help enhance that quality. 5 Trauma or Injury Scrotum or penis damage can affect semen quality in a variety of ways, but it primarily interferes with thermo- regulation, says Sheerin. "If the stal- lion is kicked and there's a hematoma (a swelling or pocket of blood) in these areas, there will be swelling, and this also insulates the testicles," he says. "If there is trauma to the spermatic cord or cremas- ter muscle and the stallion can't raise or lower the testicles (for thermoregulation), this will also have an adverse effect" on semen quality. 6 Fever A prolonged higher-than-normal temperature can affect sperm production and viability. If a stallion spikes a fever just before or during breeding season or when being collected, he might be infertile until new sperm completes its production cycle. "It takes about 60 days for sperm devel- opment, so the stallion should be checked about 60 days after the fever incident to see if he is producing normal sperm again," says Sheerin. "Often people think of reduced semen quality and fertility being associated with localized trauma to the scrotum (causing inflammation and heat), but systemic infection or anything that causes a rise in body temperature can have a similar ad- verse effect," Varner adds. "We encounter this fairly often; the horse was ill and had a fever for a few days and later developed a period of subfertility or infertility." Some horses might experience a mild fever a day or two after routine vaccina- tion. "Even though it is temporary, short- lived fevers such as this will often result in reduced semen quality," says Varner. Inoculate your stallions at least a month or two before breeding season starts. Overweight stallions have more fat insulating the testicles, which interferes with thermoregulation and, thus, semen quality and fertility. PAULA DA SILVA/ARND.NL

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