This is a photo of Impressive. The main horse who has genetically passed the disease along.
One morning, Caitlin Ryan, owner and manager of Toad Hall Farm, walked out to her barn to to feed the horses. She found Handsome, her old show horse, was having muscle spasms in his hind quarters. She thought that it was odd and that she would keep an eye on it throughout the day. As she did the barn chores she noticed that he has laid down. She went into is stall to make sure that everything was alright. She found that the spasms in his hind quarter were getting for frequent, then he started seizing. She immediately called the vet because it was very frightening to see a horse go into having a full seizure. They tested him for Hyperkalemic Periodic Paralysis, also known as HYPP.
HYPP is a genetic disorder that has been traced back to a Quarter Horse line called Impressive. This line of horses is known for doing very well in the In Hand and Halter classes. This is a big reason for why people continue to breed them. The breeding industry can be a big business especially if your line of horses is known for doing well in competition. The fact that people are not riding them adds to why it is not been bred out. There is not as big of a risk handling horses with HYPP as there would be if the line was known for a discipline that goes under saddle.
A horse with HYPP has problems with the sodium and potassium levels in their bodies. They can suffer from muscle twitches, excessive yawning and paralysis of the hind quarters as well as the heart, and lungs. The attacks can vary in severity. Some symptoms are unnoticeable but some can lead to sudden death. Not every horse who is HYPP positive shows signs. Some horses never show a sign a day in their life but others drop dead because of the disease.
Diagnosing HYPP by simply observing a horse can be very tricky. Especially when the symptoms are so similar to symptoms of colic. But the disease is very easy to test for, and is very inexpensive. It is only thirty dollars and all you have to do is pull between 20-30 mane hairs with the roots to collect DNA from. Even if a horse carries the recessive gene it can still be affected so it is important to be aware if your horse has it. A vet from the American Association of Equine Practitioners, Dr. Sharon Spier said that any horse related to Impressive should be tested as well as any horse showing any of the symptoms.
Dr. Sharon Spier was apart of a study to investigate how common HYPP throughout the horse population. She found that about four percent of Quarter Horses are affected. In another study sampling 1,000 horses of other breeds not just Quarter Horses it was most frequent among Quarter Horses with Impressive bloodlines.
According to the Equine Veterinary Journal there was a experiment conducted on nine horses who were homozygous for HYPP. Each horse had episodes where there were abnormal respiratory stertor which caused them to make a honking or rattling sound. Five of the nine had issues swallowing and 3 and out of the nine showed significant wait loss. One of the horses in the experiment was a stallion who they found to be infertile. Six out of the nine either died or had to be euthanized before the experiment was over. And all of those six horses were less than five some as young as twenty months. The other three did survive until the end of the study.
They also tested the difference between the homozygous and heterozygous carriers of this disease. They found that in the homozygous the symptoms were much more severe. At the end of the study they determined that HYPP is inherited as a co-dominant genetic disorder. This means that 25% of foals coming from a Sire and Dam that are both heterozygous would produce a homozygous offspring.
They are making some headway in the ability to manage HYPP attacks. There are many good dieting instructions that help avoid attacks from happening. One thing is to stay away from foods with high potassium, this helps their levels stay low and gives them less of a reason to get out of hand. Also avoiding food and or water depravation is key. Staying away from general anesthesia as much as possible is helpful. Exercise and frequent feeding keeps the body moving and processing. “I believe that it is important to know if your horse has HYPP because if you are riding them and they have a seizure you could be injured as well,” said Alison Hornbaker.
According to Dr. Spier it is not likely for a horse with HYPP to have an attack while being ridden. She does say that only very experienced horsemen who are aware of the symptoms should ride affect horses.
Alison Hornbaker, class of 2015 said, “a friend of mine had a horse who was HYPP positive and would show symptoms if and when he was being worked really hard in the heat. He would break out into hives and then he would have mild seizures. You could only tell by looking in his eyes and because he would stop and stare off.” Each horse with HYPP is different and their triggers can vary.
There seems to be a big question as to if breeding horses who have HYPP is ethical. As well as if it is ethical to breed horses who might have it. Is it worth spending the thirty dollars to have the horse tested or not. Some people are asking if it should be mandatory to test for HYPP before you breed. On the other hand if a breeder were to find out that one of their brood mares or stallions is HYPP positive they could be out a lot more than thirty dollars.
When asked if she thought it was ethical to breed horses who were known to have HYPP Amie Chenault, Stable Manager at Sweet Briar College said via e-mail, “as far as breeding horses who have to show–I can see both sides of that question– because some horses have it and never show a sign a day in their life and then some other have it and have to be euthanized. Also some horses have it and owners know and the symptoms can be handled by the horses diet. So I guess I am 50/50 on the question.”
The Impressive line is known for doing very well in the show ring when entered in Halter and in hand conformation classes. The risk of somebody getting hurt because they were riding them is very small because they do not have to be ridden to show.
Although Louise Goodling, Field Team Coach and Instructor at Sweet Briar College, realizes that she is not an expert and does not want to force an opinion on anybody she said via e-mail, “Personally I do not believe that breeders should breed animals that carry the HYPP gene or have other known defects or faults. If I was to breed her (Grace) to a Quarter Horse I would make sure he had been tested and did not carry the gene and if you look at paint/app/QH stallions many of them have been tested and advertise that they do not carry the gene.”
The disease was identified in 1985 and there are no regulations when it comes to breeding horses who are carriers.The test was made open to the public in 1992, but not only has the test not been used very often but the frequency of the disease has increased. Even after vets and vet schools have promoted testing for the disease it is too big of a risk for the breeders. They do not want to lose their nice mares and stallions to a disease that does not cause them too many problems after they sell the foals. The American Quarter Horse Association (AQHA) banned foals that are H/H of being registered on January 1, 2007. This still is not covering all Impressive descendants. The AQHA would like to say similar rulings in Arabian Horse Association, Pinto Horse Association, International Buckskin Horse Association, and the Palomino Horse Breeders. These are all Associations that have horses with HYPP registered.
Many believe that HYPP does not just affect the Quarter Horse industry but the entire Equine Industry throughout the United States. Handsome is not a purebred Quarter horse and Caitlin was not aware that his bloodlines went back to Impressive. Caitlin said in an interview, “I have always known about HYPP but I have had Handsome since he was young but we never did too much research on his bloodlines because he was just a backyard bred horse. I am glad that I know now and at least I can help him with diet.”
The horse industry needs to be educated about HYPP especially if the breeding of affected horses is not stopped. The safety of the horses as well as the owners is at risk until the disease becomes a more common name. The vets are definitely working on a solution and a cure or something to help with the symptoms. Until then the big Associations where most of the horses would be registered are requiring all animals to be tested and if they are positive they will not register them. This is happening in more and more of the Associations which also make the horses less valuable. If a horse can not be registered there is no real way to track where they came from. Headway is being made and hopefully there will be a solution soon.
link to a video of an HYPP attack