Well-known Tennessee walking horse trainer Jackie McConnell and several associates have been indicted on 52 counts over alleged horse soring violations.

They are accused of violating the federal Horse Protection Act. The indictment includes 18 felony counts and they are also charged with violations of the Tennessee Cruelty to Animals Statute.

The violations allegedly occurred at the annual National Walking Horse Trainers Show in March 2011 in Shelbyville and two other events.

It is alleged they conspired to violate the Horse Protection Act by transporting and showing horses they knew to be sored and also falsifying entry forms and paperwork.

The Humane Society of the United States (HSUS) said an undercover investigation it conducted led to the indictment.

The society said it was helping the Tennessee 25th Judicial District Attorney General's Office, the US Attorney's Office and the US Department of Agriculture's Office of the Inspector General with the removal of horses from McConnell's training operation.

The trainers are alleged to have used painful chemicals on the horses' front legs, using pain to force them to have an artificially high-stepping gait for show competitions.

The practice, known as soring, has been illegal for more than 40 years under the federal Horse Protection Act.

Soring is also specifically prohibited by Tennessee's animal cruelty law.

The society expressed its thanks to US Agriculture Secretary Tom Vilsack, US Attorney William Killian, of the Eastern District of Tennessee, Assistant US Attorneys Steven Neff and Kent Anderson, the US Department of Agriculture's Office of the Inspector General, District Attorney General Michael Dunavant, and Assistant District Attorney General Mark E. Davidson for the Tennessee 25th Judicial District for taking decisive action in the case.

The society said it recently completed an investigation into the training of gaited horses.

"The cruel training methods documented throughout our investigation are sickening to watch for any horse lover, and show the immense suffering horses often endure simply for the sake of a high-stepping gait," said Keith Dane, director of equine protection for the society and Maryland director of the Tennessee Walking Horse Breeders and Exhibitors Association.

"Horses entertain us and provide us companionship, and should not be subject to this horrible cruelty and abuse."

Dane is also the former president of one of the leading organizations dedicated to the humane care, treatment and training of gaited horses.

The society said several winning trainers in the walking horse industry had repeatedly been found in violation of the Horse Protection Act, yet continued to train and sore horses for customers while on suspension from showing.

It said McConnell was on a five-year federal disqualification from showing at the time of the society's investigation.

The state and federal charges against McConnell and his associates follows another recent federal criminal prosecution involving soring.

Last year, a federal grand jury returned a 34-count indictment against Tennessee horse trainer Barney Davis and three others, charging them with violations of the Horse Protection Act and related financial crimes.

Davis was further charged with fraud, wire fraud and money laundering. He pleaded guilty to several counts last November, and earlier this week a federal judge sentenced him to serve more than a year in prison.

The society said the most common form of soring involved applying caustic chemicals to the pasterns (ankles) of show horses, sensitizing the area and forcing the horse to lift its front legs high off the ground in reaction to the pain. The horses are then ridden and shown with metal chains around their ankles, which further accentuate the high-stepping action with each painful stride.

Soring can leave tell-tale scars, including tissue change, calluses, bleeding, inflammation, and skin and hair loss-all, of which are evidence of the practice.

The society called on Congress to increase funding further for the US Department of Agriculture's enforcement of anti-soring laws to crack down on what it called rampant abuse in the industry.

Congress passed a 2012 agriculture appropriations bill that increased funding for enforcement by nearly 40 per cent.