An American animal rights group has revealed footage of Tennessee Walking Horses – a breed known for its high-stepping gait – being beaten and abused.

The Humane Society of the United States (HSUS) conducted an undercover investigation and filmed a video that was then broadcast by ABC News.

The footage shows the horses being beaten with wooden sticks and poked with electric cattle prods at a stable outside Memphis. Trainer Jackie McConnell is facing a felony charge for violating the Horse Protection Act.

Warning: this video contains graphic content that you may find upsetting

The HSUS says that horses’ coronet bands and pasterns were slathered with chemicals then wrapped in plastic to make them hyper-sensitive, causing them to raise their front legs artificially high – a practice known as “soring“. The practice has been illegal for more than 40 years.

The day after ABC News broadcast the video, drinks manufacturer Pepsi dropped its sponsorship of America’s leading competition for the breed, The Walking Horse National Celebration (22 August – 1 September).

However, Pepsi has not confirmed the reason for cancelling its sponsorship.

In 2009 an organisation was set up within the Tennessee Walking Horse industry to tour shows and inspect the horses.

But the HSUS’s Keith Dane said: “This procedure of soring has been going on far too long. The industry has been able to self-police with very poor results.”

Leaders of the Tennessee Walking Horse industry claim that such cruelty is rare.

“You don’t have to do this kind of junk to win. We’re terribly against it,” said Dr Stephen Mullins of SHOW, the group that oversees inspections of the horses before major events.

However a random inspection by the Department of Agriculture at last year’s championship found that every horse tested had some sort of foreign substance around their front hooves.

Dr Mullins claims that there are innocent explanations for some of the substances found.