WASHINGTON -- Putting mustard oil, kerosene, diesel fuel and other blistering agents on Tennessee Walking Horses has long been part of the cruelty of soring -- the infliction of pain on the animals' front legs and hooves so that touching the ground causes them to recoil in agony and achieve a higher-stepping gait.
But Department of Agriculture documents show the horses frequently face a second set of chemicals as well -- those used to mask scars and numb a horse's pain to fool inspectors.
And walking horses at the Tennessee Walking Horse National Celebration in Shelbyville, Tenn. -- which starts Aug. 20 -- test positive for masking and numbing agents more often than not, leaving critics to doubt the industry's claim that at least 97 of every 100 horses are free of soring and their owners and trainers in compliance with the Horse Protection Act of 1970.
USDA's Animal and Plant Health Inspection Service (APHIS) has a long list of banned "foreign substances" its inspectors test for at events like the Celebration. They are banned because they can be used to hide evidence of soring.
The list includes many substances associated with industrial processes, such as making dyes and pesticides, bleaching wood pulp and making paper and packaging.
Some, such as o-Aminoazotoluene or anthraquinone, are animal carcinogens.
Still another, sulfur, is sometimes mixed with motor oil to make a paste that is rubbed on a horse's damaged areas to cover up soring.
And pain-blocking chemicals like lidocaine are applied in amounts calculated to keep a horse quiet during inspections but wear off in time for the pain to return in the show ring when the horse needs to demonstrate the exaggerated "Big Lick" gait, the American Veterinary Medical Association contends.
USDA records show 67 percent of horses examined at the Celebration in 2013 tested positive for substances that could mask soring. Figures for other years include 76 percent in 2012, 98 percent in 2011 and 86 percent in 2010.
"Has there ever been any sporting event with that rate of cheating?" said Teresa Bippen of Friends of Sound Horses, a St. Louis-based organization.
The masking and numbing agents wouldn't be needed if soring were as limited as Big Lick owners and trainers contend, say supporters of the Prevent All Soring Tactics Act. The proposed bill in Congress would amend the 1970 Horse Protection Act and significantly bolster USDA's ability to police the practice.
"The percentage of prohibited foreign substances found at Tennessee Walking Horse shows in recent years speaks volumes regarding the high degree of soring that still occurs within the Big Lick segment of this breed," said Keith Dane, a specialist on equine issues for the Humane Society of the United States.
Dane and other PAST Act supporters see the prevalence of substances used to hide soring as rigging the Horse Protection Act compliance statistics cited by bill opponents.
Jeffrey Howard, spokesman for the Shelbyville-based Performance Show Horse Association, one of the major groups representing the industry's Big Lick faction, declined to answer questions about the results for banned substances, saying they were based on "fundamentally flawed" information coming from "other parties," a reference to groups like the Humane Society and the USDA itself.
But John Bennett, a Shelbyville veterinarian representing PSHA, attacked the banned-substance figures in a November 2013 appearance before the House Energy and Commerce Committee, saying they were "unscientific, wholly misleading and provide no support" for the position of PAST Act supporters. In a horse-show environment, he said, it's unrealistic to think a horse's lower leg -- called the "pastern" -- and hooves could avoid trace amounts of various substances.
He and other bill opponents argue the legislation goes too far and would decimate the industry.
"We want to save a Tennessee industry that has a 97 percent compliance rate and protect these animals from the bad actors who make up the 3 percent on non-compliance," said Mike Reynard, a spokesman for Rep. Marsha Blackburn, R-Brentwood, one of the most prominent PAST Act opponents. Blackburn's office issues the comment repeatedly when asked about her opposition.
But questions about compliance rates remain central to the debate over the bill, which is stalled on Capitol Hill despite having overwhelming numbers of co-sponsors in both the House and Senate.
In a 2012, when finalizing minimum penalties for violations of the 1970 law, USDA officials said in the Federal Register that they had received public comments describing the 97 percent to 98 percent compliance claims as "meaningless." USDA officials themselves said the rates were "not in and of themselves" proof of effective industry self-policing.
While declining to discuss such criticisms, Howard, the PSHA spokesman, said the industry has adopted new standards for protecting horses that "far surpass the requirements set down by the U.S. government."
PAST Act supporters, meanwhile, say the banned substances are far from the only factor skewing the 97-percent figure.
First, the say, the rate only considers violations found by industry-hired inspectors, not those USDA veterinarians spot when they perform unannounced inspections.
Because USDA can only afford to send its own veterinarians to a fraction of the nearly 500 horse shows held annually, Congress amended the Horse Protection Act in 1976 to allow "horse industry organizations" to provide inspectors.
When USDA veterinarians do show up, they both make their own inspections and monitor the work of industry-hired inspectors. And between 2007 and 2012, USDA figures show, 61.2 percent of Horse Protection Act violations were issued at the roughly 10 percent of shows federal officials were able to attend and look over their shoulders.
Further, a 2010 USDA inspector general's report described the industry-run system as rife with conflicts of interest, another factor suppressing violation totals.
The industry-paid inspectors, it said, "understand that they will not please their employers by excluding horses from the show due to violations of the Horse Protection Act." It added "they have a direct conflict of interest with enforcing the law and regulations."
Also, the violations total is divided by the number of "entries" in nationwide shows. The distinction is important because owners often withdraw entries rather than risk an inspection that could reveal soring, PAST ACT supporters say.
Dane, of the Humane Society, says a more accurate measure would be to take the number of violations issued by both industry and USDA inspectors and divide by the number of Big Lick horses -- not other breeds -- actually inspected, not just entered. That would result in a far smaller denominator and a higher violations rate, he said.
Even with other breeds factored in, USDA figures for 2013 show 94 percent of all Horse Protection Act violations were at Big Lick events.
Said W. Ron DeHaven of the American Veterinary Medical Association at the 2013 congressional hearing: "As many like to say, this system is set up much like a fox watching a hen house -- not a good way to ensure the good welfare of these beautiful horses."