Nutrition's role in stallion fertility

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Jun 01, 2008

Obesity may be Enemy No. 1 when it comes to a stallion's libido and fertility during the breeding season — a key reason for equine practitioners to counsel their clients on proper equine nutrition, experts say.

An important indicator of a stallion's nutritional status is body condition score (BCS), a measure of body weight proportional to stature that should be taken prior to and throughout the breeding season. A stallion that is either too thin or too fat may not have the stamina to breed to a full book of mares.


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A BCS of 5 to 7 generally is considered a good target, though each horse should be fed based on its specific temperament, activity level and "ease of keeping." One that tends to lose body weight during the breeding season, for example, might do better a bit heavier, perhaps around BCS 7, at the start of the season. It is thought that obesity may lead to poor performance, cardiovascular problems and/or decreased libido in stallions.

"To me the main thing in feeding the stallion is maintaining appropriate condition," says Steve Jackson, PhD., a consultant to Bluegrass Equine Nutrition in Lexington, Ky. "More times than not, stallions are fed too much and many of the problems that we see are related to their being too fat."

Breeding stallions typically require about 25 percent more nutrition than a mature stallion's intake during the off-season, about the same as a horse performing light work, according to Pete Gibbs, PhD., professor and horse specialist for Texas AgriLife Extension Service at Texas A&M University's Department of Animal Science.

"Stallions need to be in acceptable body condition long before the breeding season starts," Gibbs says. "It's not good to try to manipulate body condition during a breeding season."

"Probably one of the big things you'd be concerned about is managing them to maintain body condition, so you don't have excessive body condition, and so they don't lose a whole lot during the breeding, because they certainly can," concurs Paul Siciliano, PhD, associate professor of equine nutrition at North Carolina State University's Animal Science Department.

"Being overfed absolutely is a problem with many stallions I have seen," says Carey Williams, PhD, equine Extension specialist at the Rutgers University Equine Science Center. "There are a lot of stallions that go into the breeding season obese. It decreases their libido and decreases their fertility."

Stallions that enter the breeding season obese should get regular exercise, increased hay and less grain, Williams says.

"Limit their access to high sugar/starch sweet feed."

One caution Gibbs mentions is that some stallions, if working hard, and depending on their "book," may lose weight if not fed sufficiently, especially Thoroughbreds booked for up to 120 mares. What's ideal? "The stallion should be in a moderate to fleshy condition; there may be a slight crease down the topline; ribs may not be seen, but can be felt; some fat slightly evident between the ribs, and the fat over the ribs feels spongy; small amounts of fat along the sides of the withers and behind the shoulders; and fat around the tailhead feels somewhat soft," Gibbs says.

"Nutritional needs may be modified according to the behavior and general activity level of the individual stallion," Gibbs suggests. The overly temperamental stallion that paces and works excessively should be fed accordingly, he adds, pointing out that pasture and/or hay are not sufficient alone, but are an important part of a total nutrition program. He suggests that 1 percent to 2 percent of body weight (BW) of good quality hay and/or quality pasture may furnish all the animal's forage needs, and that a few hours of grazing provides the added benefits of exercise and some relief from the stress of breeding.

The stallion's body condition should be monitored, perhaps weekly during the breeding season, and if weight strays too far from ideal, intake adjustments should be made to keep the animal fit, experts say.