For racehorses, the primary goal "hopefully is to enhance red-cell count, to help blood counts and increase appetite, " Dunlavy says. "You can take a horse that is a slight individual and hopefully get him to eat more; if you can do that, you increase his plane of nutrition and can get him to lay down more muscle mass. In racehorses, we don't want bulky, bodybuilder-looking horses, but you do want those horses to be lean, with good muscle mass."

Many racehorses have ulcers that affect their appetite. With many ulcer medications available, there may not be a need for ABS to enhance appetite if one can cure appetite depression with ulcer medication. "A veterinarian made that statement to me," says Soma. "Probably the cheapest way to do it (improve appetite) is to give them ABS, but the better way is to get rid of the ulcers. That veterinarian's statement is absolutely correct," Soma says.

There is some evidence regarding ABS and metabolic recovery. ABS do appear to increase the rate of muscle-glycogen repletion after exercise or a race. "They may have recovered a little faster after racing, but the data didn't say that we have a bunch of horses that ran and we gave them ABS and they were able to run them back in two weeks vs. three weeks," says Soma. "That kind of data is not available."

Because geldings have little endogenous testosterone, some feel that exogenous ABS may be beneficial to level the playing field with intact colts that have large amounts of endogenous testosterone.

"However, evidence to substantiate these anecdotal observations was not substantive," Soma says.

"The ABS have testosterone-like effects on geldings, anabolic effects that are more pronounced than testosterone itself," says Dickson Varner, DVM, MS, dipl. ACT, reproductive specialist at Texas A&M University Veterinary School.

"I had a gelding that was out in the paddock with a mare, and another gelding was turned out with them," Varner notes. "The other gelding got to kicking him quite a bit, and so I gave him a little shot of boldenone just so he could stand his own ground. In response to the ABS, he was very aggressive toward that other gelding and started mounting the mare."

"It will have an immediate effect on geldings, so that they are then less trustworthy when on ABS," Varner says. "I don't know if they're more aggressive (per se), but they do have a psychological change when on ABS, and they 'think' they are stallions. It's difficult to say what effect it has on metabolic activity in the horse, other than that."

"Regarding ABS and a gelding racehorse I had, the last thing I ever thought he needed was to get any ABS," says Stuart Brown II, DVM, reproduction specialist at Hagyard-Davidson-McGee in Lexington.

"Being that size (>17 hands), he didn't need to be carrying any more mass on that limb structure. I think all too often the anecdotal evidence about geldings needing ABS has taken precedence over what people see and judge in terms of the way individuals do, or perform, or how they mature."

Effects on behavior

ABS may trigger an increase in pre-race aggressive behavior in many horses.

"They (horses on ABS) often have more of a sour disposition and are more aggressive and unpredictable," says Sue McDonnell, MS, PhD, head of the Equine Behavior Program at the University of Pennsylvania's New Bolton Center.

"You might be walking a mare and all of a sudden, unprovoked, she bites your arm," McDonnell says.

Not that stallions won't do the same: Males and females on anabolic steroids seem to have aggression in somewhat unusual patterns and intensity. "They seem to have a short fuse for rage," notes McDonnell. "They overreact to things or react unpredictably. One day it's fine to pick up their feet and the next day they violently object.

"This behavioral inconsistency is pretty common with ABS or exogenous androgen treatment. It always rings true to me when I hear reports on the concerns about erratic behavior in humans on steroids — that's exactly my experience with horses. I'd rather be around a consistently tough stallion on his natural hormones than a mild stallion or a gelding or a mare that's on anabolic steroids. You let your guard down, and you can get hurt," McDonnell cautions.

Will ABS make a filly or colt more aggressive? "Absolutely," says Churchill Downs' Dunlavy. "But, purely subjectively, I can tell you from experience that is not the case for stanozolol. It doesn't seem to produce the personality changes that testosterone or boldenone do. I don't care whether it is a male or female, you'll see a definite male aggressiveness on those, while on stanozolol you really won't. So, for the horse with the aggressive personality, the pharmacological choice would be stanozolol or nandolone. I don't think you see it as much with those two, for whatever reason.