Ms. Mandarino did not attend the hearing, citing a death in the family. Instead, she produced statements attacking the motives of her critics and offering praise from clients, federation members and veterinarians.

Ms. Mandarino always provided “the utmost care in veterinary medicine” for her ponies, wrote Alexis G. Newman, a federation member. Ms. Mandarino also produced statements from suppliers saying they had not sold her Carolina Gold or other banned substances.

A post-mortem exam of Humble found an anti-inflammatory and a muscle relaxant, though not in excessive amounts, and no illegal drugs. In addition to emerging lung disease, the exam concluded that the pony could have died from “an overwhelming allergic response to medications or environmental triggers,” but said that was “speculative and impossible to confirm.”

In the end, the federation hearing panel dismissed Ms. Williams’s protest, saying it did not have enough evidence to decide if rules had been broken.

Ms. Mandarino filed an unsuccessful complaint against the federation’s general counsel with the Kentucky Bar Association and has filed a lawsuit accusing an online publication, Rate My Horse PRO, and various individuals of conspiring to harm her business. Rate My Horse PRO, which says it is an advocate for horses, has filed papers seeking to have that lawsuit dismissed.

A growing number of people in the horse world see another way of thinking about a horse’s behavior in the show ring. One approach that would reduce the incentive to medicate would be to change the judging criteria for hunters, said Ms. Winkel, the horse show judge and chairwoman of the officials committee for the United States Hunter Jumper Association.

This year, Ms. Winkel’s committee called for judges to stop rewarding horses for robotic conformity.

“People are realizing that it’s O.K. if horses are a little fresh and a little happy,” Ms. Winkel said, adding, “Why don’t we take a little more time and train these horses properly and educate their clients and give them better horsemen skills, other than to bring out a needle and a syringe every time we have a horse show.”