This past year we did S.T.E.M. week as one of our Hooked on Horsessm themes for summer camp. For Science day, we focused on genetics. Why genetics if we are not a breeding facility?
As a horse owner, and especially since we only use one breed at our facility, I felt it is important that our riders understand that the horse they may choose when they are ready to purchase their first horse, needs to be vetted beyond the typical vet check. They need to look at their horse’s genetics and what may possibly be lurking.
As the ability to isolate genes and track diseases improves so is the possibility of being able to determine the future health of a horse. Since we only have Haflinger horses on our facility, I will discuss their potential diseases. Bear in mind that these and others are present in many other horse breeds.
Equine Polysaccharide Storage Myopathy (EPSM, PSSM, EPSSM)
EPSM is a metabolic disorder. Horses are unable to keep their muscles working properly on what we consider “normal” horse diets. The symptoms include tying up, or weakness in the hind limbs. Some owners feel their horse is lazy because part way through the ride or lesson the horse slows down and has a hard time moving. This is because the horse cannot store, and therefore get muscle energy from carbohydrates.
This disorder is across all breeds of horses. Research shows that about two-thirds of draft type horses and one-third of light horse breeds are susceptible to EPSM. Often the best built, best temperament, best performing horses are diagnosed with it. This is a hereditary disorder that we may be inadvertently breeding into our stock.
It is treatable with proper diet. The horse is fed fat in the form of oil instead of the carbohydrates froun in grain. Any pelleted food is high in fat and does not contain carbohydrates. If not treated, this disorder may result in death.
In 2007 we were stunned when a horse that we felt was healthy succumbed to this disease within 48 hours. Once it was identified as her cause of death, we had the rest of our herd of 10 horses tested for the disorder. At that time the only way to test was by performing a muscle biopsy. The results showed that four of our horses also had this disease. There is now a DNA test that can be done using the hair root from the horse’s tail to determine if the horse has this disorder.
Squamous cell carcinoma
This form of eye cancer is the second most common type of tumor in horses and the most frequent eye tumor. The tumor typically develops in non-pigmented areas of the skin and the eye. It is frequently found in Appaloosas and color-dilute breeds such as Belgians and Haflingers.
Early symptoms are a reddening, roughening or ulcerating area. Treatment involves surgically removing the tumor through one of many means. Chemotherapy may also be an option. If left untreated the tumor can spread behind the eye, into the sinuses, and ultimately the brain.
Once treated, the horse needs to wear an ultra-protective fly mask during the peak sunlight hours since exposure to the sun’s ultra-violet rays can trigger this disease.
In 2014 a tumor appeared in one of our horse’s eye. We had it removed and, because we did not use the horse for our program, we sold him with full disclosure. This spring we discovered a smaller tumor in the eye of two of our horses. We had the tumor removed and treated both horses with chemo for one month. We keep fly masks on both horses during the day. To date, both are doing well.
The interesting aspect was that these horses were all full brother/sisters. All three of them developed squamous cell carcinoma in the right eye. Coincidence or hereditary?
The University of California, Davis has recently developed a DNA test to determine if a horse is susceptible to squamous cell carcinoma. We will definitely be taking advantage of this test and, should any other horses show susceptibility, they will also be sporting fly masks all year round.
Seeing that both of these diseases, along with many others, are hereditary, we can’t help but urge breeders to have their horses tested, then, decide whether breeding the horse is the right thing to do.
EPSM only requires ONE of the parents to have the disorder to pass it on to an offspring. With squamous cell carcinoma, breeding horses even if one is heterozygote (R/N), risks producing horses that can be affected with this disease.
For us, we already test any horse that we acquire for EPSM. The test for squamous cell carcinoma will now be added to the vet check list.