(CNN) -- A top trainer in the fabled Tennessee walking horse industry has pleaded guilty to a charge of cruelty to animals and has been banned for life from the most important horse show for the breed.
Jackie McConnell had been charged with 52 counts of violating the Horse Protection Act but pleaded guilty to only one in a plea agreement with federal prosecutors in Chattanooga.
The charges stemmed from a graphic undercover video made by a Humane Society of the United States investigator that shows McConnell and his stable hands at Whitter Stables of Collierville subjecting show horses to practices that were banned 40 years ago.
The video shows horses being struck with sticks and subjected to "soring," an illegal process in which chemicals are placed on their lower legs in an effort to induce the signature Tennessee walking horse high-stepping gait known as the "big lick."
According to the indictment, "soring is a cruel and inhumane practice used to accentuate a horse's gait in order to gain a competitive edge in horse shows." Chemicals and other irritants on a horse's ankles and forelegs cause it to lift its front feet and shift its weight unnaturally to the hind legs in order to relieve the pain.
McConnell and the other trainers applied a thick, yellowish substance called "the balm" on the front pasterns of a horse named Moody Star, the court documents said. The horse was seen in the video picking up his feet in pain. Later, McConnell rubbed castor oil on the back of Moody Star's pasterns to "peel off skin."
Moody Star was later taken to a show, and documents for the horse were falsified, prosecutors said. Other horses were similarly abused.
The Humane Society said its investigator documented "stewarding" -- training a horse not to react to pain during official show inspections of their legs for soreness -- by striking them in the head when they flinch during mock inspections.
The video also shows a writhing horse being subjected to a whip at McConnell's barn. Another receives an electric shock to the head.
"The video showed the horses, in obvious pain, which appear to be having trouble standing and being whipped until they did stand," prosecutors said in the plea agreement Tuesday.
McConnell's staff -- Jeff Dockery, John Mays and Joseph Abernathy -- were also charged. Mays and Abernathy have also pleaded guilty. Dockery has a plea hearing in June.
Soring "has been an open secret in Tennessee for years," said Jonathan Lovvorn, senior vice president for litigation and investigations with the Humane Society.
The video was filmed in spring 2011 by an investigator who worked two months as a stable hand at McConnell's barn, according to the Humane Society. It was first featured last week on the ABC News program "Nightline."
It raised questions of how pervasive the training techniques are despite recent prosecutions and investigations by the U.S. Department of Agriculture, which enforces the Horse Protection Act.
"There obviously is a huge problem," Lovvorn said. "In the competition to get this unnatural gait, trainers are using banned substances to cheat."
The walking horse gait, known for its smoothness, was originally devised for Southern plantation owners to inspect their lands in comfort.
Horse show judges value the exaggerated gait, and shows in Tennessee and elsewhere annually draw thousands of spectators.
The Tennessee Walking Horse National Celebration said its actions against McConnell were unprecedented.
He was suspended for life, is banned from entering the organization's grounds and was removed from its Hall of Fame.
"This action is the strongest we can take and it clearly reflects our disgust with the actions of Mr. McConnell," said Doyle Meadows, CEO of the organization. "His actions are not reflective of the Tennessee walking horse industry, and we in no way want him associated with our show."
PepsiCo said last week it was pulling its sponsorship of this summer's Tennessee Walking Horse National Celebration.
Asked if the sponsorship decision was in response to the 2011 video, PepsiCo spokesman Vincent Bozek said, "That's all we're saying." The decision was made Wednesday.
The president of a Tennessee horse industry organization, condemning the "disturbing" video, told CNN there is a stringent inspection process at shows.
"I think it's sad that a corporation like Pepsi would go out because of the action of one person and one training barn," said Stephen Mullins of S.H.O.W.
Lovvorn told CNN the Humane Society shared the video and results of its investigation with federal prosecutors before the indictment was returned earlier this year.
McConnell will be sentenced on September 10. He faces a maximum five-year prison sentence and a $250,000 fine. Mays and Abernathy face up to a year in prison and a $3,000 fine.
In separate cases, a seven-month investigation by the U.S. Department of Agriculture resulted in at least four other Tennessee men being sentenced this year for horse soring violations.
One defendant sentenced to 12 months in prison and a $4,000 fine described how chemical irritants, chains, bolts and other devices were used to bring about the exaggerated gait.
"He stressed the pervasiveness of soring in the gaited horse industry and testified that horses 'have got to be sored to walk,' " according to a news release from the U.S. attorney for the Eastern District of Tennessee.
S.H.O.W., certified by the U.S. Department of Agriculture, handles inspections of Tennessee horses at events.
Mullins, a retired equine veterinarian, said self-regulation by the industry has led to three lifetime and 150 one-year suspensions for soring and other violations of the Horse Protection Act.
Trainers shouldn't rely on soring to train horses to hit the "big lick," said Mullins, acknowledging that the industry still has problems. "I was given one charge (task). Get rid of the sore horse. I think we are well on our way."
One painless training technique, he said, is to fit pads, about 3 inches tall, below the horse's hoof.
"It can change the way the horse lands on its foot," according to Mullins. "It requires him to exaggerate and keep his foot up for a longer period of time."
S.H.OW.'s oversight, however, does not extend to training facilities and barns.
"Soring is a way to take a horse that is not very good ... to make him look good," Mullins said. "Do I think it goes on around the trainers who show routinely with me? No sir, I do not believe it does."