An Ounce of Prevention: AQHA 5-panel stallion test helps reduce chance of disease
January 18, 2018
American Quarter Horse Association World Champion stallions such as Impressive and Poco Bueno have passed on to thousands of registered offspring their athletic ability, good conformation, easy-going dispositions and innate cow sense. But, underneath the athleticism and refinement, these horses, among others, have passed on something more: genetic diseases.
In 2015 the American Quarter Horse Association began requiring a five panel test for all breeding stallions in order to deter owners from breeding stallions who may unknowingly be passing genes for certain diseases onto their offspring. The idea for the testing was first recommended by a member at the annual convention that year, which was subsequently approved by the board of directors.
"These diseases are prevalent in the American Quarter Horse and they felt that, with the tests now available, it was and is important that the horses be tested so that stallion owners and mare owners who choose to breed to those horses can make responsible breeding choices," says Tammy Canida, director of registration operation for the AQHA.
While there are many equine diseases, it was determined that GBED (glycogen branching enzyme deficiency), HERDA (hereditary equine regional dermal asthenia), HYPP (hyperkalemic periodic paralysis), MH (malignant hyperthermia) and PSSM (polysaccharide storage myopathy) were of greatest concern.
No actions are taken by the AQHA against horses that come up positive on the test, which has been 25 percent of all horses tested as of November 2017, but the AQHA hopes that owners of affected horses will take the information and use it wisely.
"Our main purpose is to educate," Canida says. "To let owners know they have a horse that may or may not have a condition, so that they can either know how to treat it if it needs treatment or care, or maybe know what to breed or what not to breed if they are positive for any of these diseases."
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Lisa Fulton, owner of Fulton Performance Horses, has seen the benefits of the 5-panel testing in her own stallion barn, saying that she now has three generations of stallions, A Streak Of Fling, A Dash Ta Streak and a colt from the latter, who are each negative for diseases.
"We've only been two years into this and I think honestly, where are we going to be in 20 years down the road, when everything we've got has been tested," she says. "We'll be a lot further down the road than we are today, and I feel like we've come a long way today."
Requiring five-panel testing of mares is not off the table for the future according to Canida, but currently there is no talk of it. Still, the AQHA does encourage members to test their mares and utilize the tools available when making breeding choices.
Fulton has used the fact that her stallions are negative as a marketing tool as well, noting on her ranch's website the test results, and she says that she has considered voluntarily testing her mares too, because she is concerned that testing the stallions only touches on half of the problem. According to Dr. Charlie Scoggin of Rood and Riddle Equine Hospital, that could be true.
"The thing is, if your stallion is negative, then the risk of him propagating that to his progeny is zero. The rest would be then up to the mare," Scoggin says. "I think it's a very useful test and I think it will protect breeders in the future so that they don't sink a lot of money into a horse that's going to have some sort of genetic defect. I also think it's better for the horses in the future because some of these diseases can be pretty darn nasty."
For GBED, some cases may be unknown, as they result in abortions, stillbirths or early death of the affected animals. If foals make it through birth, they are prone to muscle issues. Tying up is the biggest clinical sign which will, of course, adversely affect performance of the horse. GBED is considered recessive, so both the sire and dam would have to carry it to see a true clinical case. It can be managed with diet and nutrition to some extent, but according to Scoggin, that is not 100 percent effective.
HERDA is also a recessive disease that primarily causes skin lesions because the tissue below the skin's surface cannot form proper connections. As a result, affected horses are prone to skin sluffing, open wounds and all types of skin lesions. HERDA does not always manifest early in life, Scoggin says he has seen it in horses up to two years of age.
"It is a fatal disease, for lack of better term," Scoggin says. "There is no treatment and you can't do anything with them."
Research has shown that HERDA can be traced back to Poco Bueno and his sire, King, two well-known Quarter Horse sires.
Another famous Quarter Horse sire, Impressive, was identified as an original carrier of HYPP. In horses affected with this disease, an increase in circulative fat in high concentrations leads to horses who go down and are unable to rise. Scoggin says that depending on the case, horses will show muscle rigidity, or flaccidity. With HYPP, it only takes one of the parents with the gene to pass it on. The disease not only affects muscles, but the heart as well, so continued HYPP attacks will eventually cause heart failure.
"It's pretty much a man-made disease from what we can tell," Scoggin says. "The gene for HYPP is closely associated with increase in muscle size, a trait that was bred into them, especially in halter horses like Impressive. While they were thinking that they were breeding bigger muscled horses, in fact, they were also adding HYPP to the equation as well."
The rarest of the diseases on the five-panel test is MH. According to Scoggin, this disease is usually induced when a carrier horse is exposed to a certain anesthetic agent which is no longer used in North America, halothane. MH leads to paralysis and cardiac arrest, as well as detrimentally high fevers.
The final disease on the panel, PSSM, is both muscle- and skin-related. It can lead to constant twitching, muscle weakness, reluctance to move or tying up. Dietary management can be somewhat effective, but will not completely erase signs of the disease.
Even though these diseases may be treatable, except for HERDA, Scoggin says owners should consider all the costs involved before knowingly breeding affected horses. Direct costs, such as a special diet, proper management and professional care from someone who can spot signs of an impending HYPP or GBED attack will add up over time. Indirect costs, like a well-bred horse not living up to its athletic potential, should also be considered.
"Then you have emotional costs associated with the disease," he says. "You care for this animal for a couple years and then, suddenly, they go down, they can't get back up and you have to euthanize him or her. That can take a toll emotionally on people and I don't think you can discount that."
Even a stunning pedigree is not worth it for Fulton to knowingly breed a diseased horse it if it means potentially allowing a genetic disease into her horse program.
"I don't want to have HERDA and I don't want to have PSSM," she says. "I just can't do that to my animals."