What is "Soring"?
SORING is a painful practice used to accentuate a horse's gait. This is accomplished by irritating the forelegs through the injection or application of chemicals or mechanical irritants.
As a sore horse tries to escape the pain in his front feet and lower legs, he snatches them up quickly, which gives the "desired effect" of tremendous lift in the front, known as the "big lick." Meanwhile, he tries to take as much weight as possible off his front feet by shifting his weight to his back feet, squatting down in the rear as he reaches beneath himself with his hind legs. The resulting gait has been described as "the praying mantis crawl." 
How did soring get started?
THE ORIGIN OF SORING dates back to the early heyday of the Tennessee Walking Horse breed. Not long after the breed association was formed in 1935, Walking Horses shot to fame. Prices skyrocketed as the horses became an all American symbol for the media. But with recession in the 1950s, the Walking Horse industry hit a slump.
Stories differ, but it was around this time that a showman discovered that either mustard oil, being used to treat a hoof ailment, or kerosene used to clean some road tar off the lower legs, caused his horse to step livelier. Come the regular Saturday night show, this horse snapped his feet off the ground like they were on fire. Wild-eyed, he all but flew around the ring, barely setting a foot on the ground before snatching it back up again. The crowd loved it. Experimentation followed. Then imitation. Before long, "the fix" was in.
The spectators loved the action, the judges pinned the flinging feet, the show managers hired the judges that kept the spectators coming and a vicious cycle was established.
How are horses sored?
PAIN combined with long toes, heavy shoes, extreme bits, a rider sitting far back on the horse, and - never forget the heart and substance at the center of it all - a horse that keeps on trying despite all of that, creates the spectacle of the sored show horse.
While flat shod horses with naturally good movement can comfortably perform this crowd-pleasing gait, it takes both natural ability and considerable time to properly train and condition the horse.
Mechanical soring methods include use of excessively heavy weighted chains, use of tacks deliberately placed under the shoe into the "white line" or quick, of the hoof. Chemical controversial soring methods include the application of caustic compounds to the front legs to make it painful for the horse to put the full pressure of his weight on his front feet.
MECHANICAL soring can be just as damaging and painful as chemical soring.
"Stacks" up to 5" high and filled with a variety of substances for added weight, are attached to the front hooves, causing the horse to stand perpetually in an elevated, unnatural position. This type of shoeing causes chronic, constant pain. Heavy Plantation shoes weighing up to 5 lbs. are also used
Stacks can vary in height. They are usually made of plastic, although some may be made of leather. Stacks have a metal band that runs across the hoof to help keep them on the horse's foot. Stacks may be up to 4" thick in the heel and no more than 2" in the toe.
The band that holds the stack cuts into the hoof and may wear a slot into it. However, it is a common practice for a trainer to loosen the band when the horse is not being exercised, thus eliminating this problem. It is also dangerous if a horse wearing stacks tears off a shoe, as the stack will come off and the band may rip into the hoof and tear off a good part of the hoof wall.
Known as "action devices," chains worn around the pasterns can range from the mildly annoying to the extremely painful. Alone, the six-ounce chains accepted in the show ring may not harm the horse, but horses sored with heavy chains or chemicals prior to the show date can suffer intense pain in the ring as the lighter chains repeatedly bang against the sore area.
Pressure shoeing is a harder to identify, yet effective, method of torture. The hoof wall is filed down near the quick, which causes the sole to come into direct contact with the metal shoe, causing excruciating pain each time the horse puts weight on the foot. Another technique is to add a welded bead of metal to the under side of the shoe so that it digs into the hoof at each step. Pressure shoeing was actually abetted by at least one shoe manufacturer that made plantation shoes higher on the inside than on the outside, causing uneven pressure and resulting soreness.
Other tricks include placing ball bearings or golf balls cut in half between the pad and the hoof, and placing "V" springs, wrapped with a wad of black electrical tape, over the tip of the frogs to bruise the soles, and removing them just prior to the show.
Similar to the above is road foundering. The hoof wall may be rasped away nearly to the quick and the shoe nailed on. The horse is then ridden up and down a hard surface, like the roadways on or near show grounds, until its feet are sore. The next time you see an exhibitor "warming up" on the roadway, take note.
CHEMICAL soring involves using chemical agents such as mustard oil, diesel fuel, kerosene, salicylic acid, crotonal or croton oil, collodion, and others, on the pasterns, bulbs of heel, or coronary band of the horses. The resultant burning or blistering causes the horse to snatch up his front legs, accentuating his gait. These chemicals are harmful, toxic and sometimes carcinogenic. Trainers must use a brush and wear gloves when applying them. The area may then be wrapped in plastic (see below) while the chemicals are absorbed. 
Probably the most popular soring agent is mustard oil, or allyl isothicocyanate. Unlike the mild spice you ooze over hotdogs, this yellow liquid is nasty stuff. It is a highly toxic carcinogenic (cancer causing) mutagen (agent that causes inheritable genetic alterations). It absorbs through the skin and into the tissue beneath almost instantly, causing blistering and severe burning. 
Clever "trainers" combine it with Dimethyl Sulfoxide (DMSO, an absorption enhancer) to help it absorb through the skin even more quickly, and then wrap the area with plastic wrap covered with leg wraps to let it "cook", usually overnight. Exposure can cause convulsion, muscle contractions, gastrointestinal changes, rapid heartbeat to heart attack, fertility problems and fetal death.
In people, a good whiff can cause coughing, pulmonary edema, headache, nausea, vomiting and worsen asthma. When a package of mustard oil was accidentally dropped in a post office, after having been illegally mailed by a trainer to farm, the building had to be evacuated and postal employees hospitalized. Horses who are chemically sored not only suffer immediate pain, but can also sustain internal damage of the nervous system and organs.
How can you tell when a horse has been sored?
HORSES that demonstrate an abnormal sensitivity or insensitivity are suspected of being sored. The horse may incur swelling, tenderness, abrasions, bleeding, and oozing of blood or serum. Particular attention should be paid to the area of the coronet band, the area above the hoof, to the front and rear pasterns, and to the bulb of the heel, favorite places for chemical soring.
A distinctive scarring pattern is a tell-tale signs of soring, and therefore may be covered up by a dye, or the horse's legs may be soaked in salicylic acid before the animal is stalled (as many can not stand up after the treatment) while the skin of the scars slough off.
It is crucial to understand that there are different levels of being "sore" - from sensitivity to agony.
Here are some telltale signs:
- Tenderness or swelling on both front feet, or even the hinds. Soring is always bilateral.
- Scars or granulated bumps along the pasterns or near coronet band.
- Abnormal, wavy hair growth (following acid treatment) in pastern area.
- Horse resists handling of feet.
- Horse lies down frequently for extended periods.
- Horse shifts weight to hind feet, stands with all fours together, as if "on a quarter."
- Exaggerated gait with characteristic pause at breakover (highest point of stride) as horse hesitates before returning sore foot to ground.
- Oozing of blood or serum from pasterns.
- Drags front toes, because of the pain of the concussion upon set down.
- Hocks carried low to the ground and twisting towards the outside when moving.
- Horse has difficulty walking, falling, resistant to get up. 
What types of horses are sored?
THE TENNESSEE WALKER, also known as the Tennessee Walking Horse, as well as other high-stepping breeds, are the most frequent victims of soring. Tennessee Walkers were originally bred to carry plantations owners while surveying their lands.
Exceptionally well-mannered and easy to train, they are noted for their unique four-beat "running walk." They appear to sit on their hind legs, lifting their front legs high off the ground.
When does the soring start?
Training often starts young. In the padded ranks, yearlings are fitted with a colt "package" - a pad, wedge pad and a keg shoe - to get them used to the shoes, or to compete in conformation classes.
Horses are often under saddle before the age of two, years before their bodies have completely formed, before vulnerable bones have fused and before young minds have developed.
"Training" may consist only of saddling and a quick lap up and down the barn aisle, then "fixing" to adjust the gait. But conditioning and regular riding are not always part of the program. Rather than spend hours a week over a period of years to develop the classic running walk gait of the breed, some settle for soring.
The rationale is simple: "Time is money. Why take months to train a horse, when you can fix them in a fraction of the time?"
Is soring legal?
IN THE EARLY 1960s outrage over soring helped to mobilize the equine welfare movement. In 1966 the American Horse Protection Association (AHPA) was founded to address two issues: the treatment of feral horses on public lands and the prevalence of soring. Three years later Sen. Joseph Tydings (D-Md.) introduced federal legislation addressing these issues, and in 1970 the Horse Protection Act (HPA) was passed by Congress. 
The HPA prohibits the transport, sale or exhibition of sored horses. The law extends protection to all breeds, but the regulations put in place to implement it recognize that Tennessee Walking Horses, Racking Horses and other gaited breeds are most frequently subject to soring. USDA's Animal and Plant Health Inspection Service (APHIS) is charged with enforcing the act with a budget that cannot exceed $500,000 a year. 
The regulations also established a designated qualified person (DQP) program, allowing knowledgeable horsemen, such as veterinarians, farriers and trainers, to be certified to check horses for soring. Specifically, the USDA certifies Horse Industry Organizations (HIOs), and they in turn certify inspectors who check horses before they compete and reinspect the top finishers after each class. 
The horse inspection process is outlined in regulations and the so-called operating plan, a voluntary contract between some horse industry organizations and the government that has been challenged and changed many times over the years by the show industry. Under the current plan, evaluations of show horses include these components:
- General appearance. The horse's condition and expression are assessed for signs of pain. Are his flanks tucked up or his nostrils flared? Does he breathe heavily even without exercise?
- Locomotion. The horse is walked on a loose rein, usually around a cone, away from and toward the inspector, who observes him for signs of pain.
- Physical examination. The inspector palpates the front legs from knee to hoof, paying close attention to the pastern and fetlock to detect a pain response, inflammation or scarring. The hooves, especially the heel bulbs, also are checked for tenderness. In addition, inspectors assess shoes, pads and action devices for compliance with Horse Protection regulations.
- Compliance with the scar rule. One of the most controversial issues regarding the inspection process is the rule that states that "bilateral pastern scars"--scars on both forelegs--can constitute a soring violation.
Horsemen complain that the language specifying which scars are soring-related is confusing and difficult to interpret, in particular since some areas of "uniformly thickened epithelial [skin] tissue" are permitted on the lower legs. To help clarify the rules, the USDA released a 23-page document titled "Understanding the Scar Rule." 
Some trainers can bypass inspectors by "stewarding," or teaching the horses not to react to the pain that palpation may cause, by severely punishing the horse for flinching after the sored area is palpated. Trainers may also time the use of the agents so that it will not be detected when the horse is examined, but will be in effect when the rider goes into the ring.
Others use topical anesthetics, which are timed to wear off before the horse goes into the show ring. Many trainers that sore will also leave the show grounds when they find that DQPs are present.
In 2006, however, due to new techniques in both soring and detection, the USDA has begun a larger crackdown on soring within the TWH industry.
A new device known as a sniffer (also used to detect the chemical presence of bombs in airport security) is now being employed where swabbed samples are taken from the horse and then "sniffed."
AT THE 2006 Tennessee Walking Horse Celebration, the dispute between trainers and USDA inspectors came to a head. The inspectors disqualified 6 of 10 horses from showing on the night of Friday, August 25. The trainers denied soring and challenged the monitoring methods. The result was that the celebration classes were canceled that evening and the following morning, Saturday, August 26. At that point, the monitors and trainers reached a temporary agreement, allowing the celebration to continue Saturday evening. Canceled classes were rescheduled. However, a more permanent agreement on monitoring methods still needs to be negotiated, and trainers and inspectors continue to meet. 
Trainers who oppose this practice have formed and joined alternative breed organizations, including the National Walking Horse Association (NWHA) or Friends of Sound Horses (FOSH). Both of these organizations promote the sound Tennessee Walker.
 -  "More than Sore," compiled by Rhonda Hart Poe
 Equus Special Report: "Why Soring Persists".
 -  Id.
 "Horse Show Ends in Uproar Over USDA Inspections," By Theo Emery, The New York Times