Editor's note: This article is part of TheHorse.com's ongoing coverage of topics presented at the 2012 Alltech Symposium, held May 21-23 in Lexington, Ky.
While some genetic disorders require very specialized management or even euthanasia, others can be managed at least partially via nutrition. During a presentation at the 2012 Alltech Symposium, held May 21-23 in Lexington, Ky., one researcher gave an inside look at how diet can help control some genetic problems.
"Equine practice has recently embraced nutrigenomics, in which a horse's nutritional requirements are tailored to its individual genetic make-up," explained Stephanie Valberg, DVM, PhD, director of the University of Minnesota Equine Center. She discussed two disorders that can be managed nutritionally--polysaccharide storage myopathy (PSSM) and hyperkalemic periodic paralysis (HYPP)--with attendees.
The Best Treatment: Prevention
Valberg first discussed the genetics behind these disorders and how to prevent them from happening in the first place. Many genetic disorders are dominant, meaning that the genetic disease can be passed on to offspring if only one parent is affected. Others are recessive, meaning both parents need to carry the abnormal gene for an offspring to be affected. Carriers are often clinically normal. Thus, it's important to test mares and stallions for genetic disorders before breeding to decrease an offspring's likelihood of being affected.
Managing Diseases
PSSM--This disease is characterized by the abnormal accumulation of the polysaccharide glycogen--long chains of sugar molecules used for storing energy--in the skeletal muscles. The disease can be debilitating and life-threatening. Valberg said it affects more than 20 breeds of horses and is common in Quarter Horses and some draft breeds.
As a result of the abnormal glycogen accumulation, horses with PSSM can develop muscle pain, stiffness, and azoturia (tying-up) after exercising at the walk and trot for as little as 15 minutes, she said.
To manage PSSM horses nutritionally, Valberg suggested avoiding feed with a high starch and sugar content to reduce the amount of glycogen in the muscle. Instead, she recommended feeding a hay with less than 12% nonstructural carbohydrate content and a high fat concentrate to increase the amount of circulating free fatty acids in the horse's bloodstream and muscles.
Valberg noted that exercise is key to managing horses with PSSM: "Feeding special foods won't work if you don't exercise the horse." For overweight horses, rather than feeding fat she suggested fasting the horse for six to eight hours before exercise to increase circulating fatty acids.
HYPP--The first major genetic disorder identified in the horse, HYPP disrupts the function of tiny gateways in muscle cell membranes called sodium channels. Instead of opening and closing normally, they stay open during a HYPP episode, allowing an uncontrolled flow of sodium into and potassium out of cells. This alters the cells' normal functioning, which results in the signs of HYPP--weakness, muscle twitching, shaking, trembling, and paralysis of upper airway muscles. The most severe threat to affected horses is death from respiratory obstruction or irregular heartbeats.
To manage these horses nutritionally, Valberg recommended feeding a diet that includes less than 1% potassium in the total diet. She also recommended turning horses out on pasture and feeding grass hay, beet pulp (without molasses), oats, corn, or barley, as all these options have low potassium levels. She cautioned to avoid alfalfa, soy bean meal, and feeds with molasses, as these options can contain too much potassium for HYPP horses to consume safely.
Take-Home Message
The best treatment method for genetic disorders is prevention, so ensure mares and stallions are disease-free before breeding. In the event a horse is affected with a genetic disorder, work with a veterinarian to develop a proper diet that will help best manage his condition.
Disclaimer: Seek the advice of a qualified veterinarian before proceeding with any diagnosis, treatment, or therapy.
