A federal grand jury indicted four people charged with abusing horses used in Tennessee Walking Horse competitions.

The 34-count superseding indictment against Barney Davis, 38; Christen Altman, 25; Jeffrey Bradford, 33; and Paul Blackburn, 35, adds charges to the original indictment, which alleges the defendants violated the federal Horse Protection Act by "soring horses and falsifying forms and other related paperwork."

In the practice of "soring," bolts or other objects are driven into horses' hooves or chemicals are used to "produce pain and sensitivity to alter the gait of a horse," according to the release.

Davis and Bradford live in Lewisburg, Tenn., and Altman and Blackburn live in Shelbyville, Tenn., according to a U.S. attorney's office release.

The indictment claims that, as a part of Davis' horse training operation, he and Altman boarded horses at Monopoly Farm, formerly known as Hidden Cedar Stables, in Lewisburg under the auspices of training them in a manner conforming to the Horse Protection Act.

From about 2002 to March, Davis directed workers insert bolts in horses' feet and tape the feet to blocks, then mask or remove the devices prior to inspections at horse shows, the indictment states.

"Some of the alleged conduct of the defendants contained in this superseding indictment constitutes federal felonies, if convicted," U.S. Attorney Bill Killian said in the release.