Effects on reproduction

In female horses, large doses of exogenous TES eventually caused total suppression of all reproductive activity and the development of stallion-like behavior and aggression. Most stallions have reduced reproductive capacity. After administration of ABS to geldings and mares, stallion-like behavior was observed, "indicating residual androgenic activity of ABS. Mares with ABS show stallion-like behavior, including mounting, teasing and aggressive behavior toward other horses," McDonnell says.

"Though it depends on what age they are treated, theoretically if they started early enough, with a weanling or yearling ABS could delay puberty," she adds.

With colts/stallions treated with ABS, response is not black and white," says Varner, who examined many stallions at the racetrack in preparation for their first year at stud. "We had evidence of stallions with a history of treatment with anabolic steroids having small testes," Varner says.

Sometimes the testes do not grow even after the horse is removed from a race setting, he explains, while at other times there is a significant increase in testicular size. "It's difficult to say what's attributable to the anabolic steroids, and to other factors associated with their racing career," Varner says.

It appears that boldenone is more likely to be detrimental to semen quality than stanozolol. "It (boldenone) was found to cause a more rapid reduction in testicular size than stanozolol when given to pony stallions," notes Terry Blanchard, DVM, dipl. ACT, a reproductive specialist. However, both caused significant decreases in testicular size, seminiferous tubule diameter, sperm production and size of Leydig cells within the testicular interstitium, compared to non-treated control stallions. This difference was believed related to a longer half-life and different chemical structure (i.e., boldenone more closely resembles the chemical structure of testosterone).

No controlled trials have been conducted with boldenone and stanozolol to see which has the more profound effect, Varner says.

"Long-term use of anabolic steroids with young Standardbred and Thoroughbred colts/stallions will interfere with semen production," says Michelle LeBlanc, DVM at Rood & Riddle. However, most horses leaving the racetrack have fair to good quality semen within six months, she says. "We have had discussions of poor-quality semen in some horses in the first two to four months after racing — whether it's due to anabolic steroids or the stress of living the racetrack life. I don't think that we can blame it all on steroids. Too many horses turn around too quickly after being let down."

Fillies/mares

With fillies or mares that have already started cycling, ABS often do not actually stop the mare from ovulating but do change behavior so that the filly or mare doesn't show estrus and becomes studlike. "She tends to fight with the stallion even though she may have a follicle on her ovary all ready to ovulate; she becomes very difficult to breed," McDonnell explains. Some need to be off steroids as long as six months before they resume normal estrus and discontinue the male-type behavior.

Even without ABS, if a mare comes right off the racetrack to become a broodmare it may be difficult to get her pregnant in that first season. If she comes off in summer or early fall and has six months or so before breeding, most will return to normal sexual behavior, McDonnell explains.

"It might be a function of body weight, just as women athletes don't cycle when they get too fit and thin. We took mares and treated them with doses of anabolic steroids so that we could follow them and know how much they received, and followed their ovarian activity," says McDonnell. "It was expected that from those doses the mares would stop ovulating. Some continued to ovulate, but they were not as regular as the control mares."

McDonnell and colleagues published a paper of how one could make a "teaser stallion" out of a mare with anabolic steroids, on doses similar to those given on the racetrack. Many of the mares would mount other mares. "You can pretty much turn them into a 'stallion,' " McDonnell says.

Given some time, mares removed from racing will return to normal as medication is removed from their system, and will return to normal estrus behavior, says Brown. "It can be frustrating for breeding managers and owners, though, because it often takes a while for them to settle."

ABS for racehorses?

"It was really our organization that spearheaded the drive to start developing the model rules (to regulate ABS) now being adopted by the various jurisdictions," says Scot Waterman, DVM, executive director of the RMTC.

Evidence was growing that anabolic steroids were being overused and abused in racing. Also instrumental was the threat of congressional intervention, starting with a bill put forward by Rep. Ed Whitfield (R-Ky.).

That bill would prohibit the use of anabolic steroids in any horse that ran in a race subject to simulcast wagering under the Interstate Horseracing Act.

"Most of the people we talked to at the time didn't think the bill had much chance of success, but it was still clearly a shot across the bow. We needed to deal with this as an industry, or Congress was going to do it for us," says Waterman.

"They (ABS) need to be eliminated in racing," Dunlavy argues. "The bottom line is, nobody wants anabolics in football or baseball players and to have horseracing as the only major sport out there allowing them — well, I think it's bad," Dunlavy says. "It creates a poor public impression of the game and the industry."

"I don't think they're necessary," agrees Rick Arthur, DVM, executive director of the California Horse Racing Board (CHRB). "Our position is that there may be times when legitimate use would be warranted (horses rehabbing from an injury, recuperating from debilitating disease, chronic pleuritis, pneumonia).

"But that is quite different from racing on anabolic steroids. ... What we propose is a regulation that would allow some use of anabolic steroids for a limited number of days prior to racing."

"Horses around the world race without anabolic steroids and very successfully," Arthur says. "In terms of the sport, I doubt that many people are aware that we don't regulate anabolic steroids. It's going to be difficult to convince the public that Barry Bonds can't have them, but these animals ... need them. It's something the racing industry is going to have to face and is facing I think quite successfully."

Kane is a Seattle author, researcher and consultant in animal nutrition, physiology and veterinary medicine, with a background in horses, pets and livestock.