Equine Polysaccharide Storage Myopathy (EPSM) is a glycogen storage disorder affecting skeletal muscle function. Diets high in carbohydrates (starch) contribute to the onset of symptoms but do not cause the disease.
EPSM is primarily found in Warmblood, Draft Horses, Quarter Horses (including Paints and Appaloosas) and mixes of these breeds with other breeds.
In Quarter Horses there is a genetic correlation and inheritance is possible. The incidence is not gender specific.
Horses with EPSM will always be more prone to muscle soreness. The most common clinical signs are painful firm muscles (especially along the back and hindquarters), reluctance to collect and engage the hind end, stiffness, short stride, gait abnormalities, weakness, and muscle atrophy. EPSM can progress to tying up (exertional rhabdomyolysis (ER), Monday Morning Disease) where there is severe muscle trembling and muscle damage that can lead to secondary kidney damage and even death.
Blood work with elevated muscle enzymes (CPK, CK, AST) indicates muscle damage, but not the specific cause. To confirm EPSM, a muscle biopsy is required. Management of horses with EPSM involves exercise and diet. Keeping the horse fit to improve oxidative metabolism and fat utilization for energy is important. This involves a very slow build up in the exercise program realizing that the duration is as important as the intensity of the work. These horses should have minimal stall confinement and get daily exercise. The diet for EPSM horses should be low sugar, low starch with high fat as the primary energy source.
Functionally, these horses do very well when they are not given grains and sugars, including those used in treats. While a diet with a very high fat content is important, the quality and digestibility of those fats are critical. Good fats that are not inflammatory such as flax, hemp and coconut oil offer great support and energy. EPSM horses often do well on a primarily alfalfa hay. They benefit greatly from supplemental gut support and digestive enzymes to ensure proper digestion. A vitamin/mineral supplement that supports the horse’s endocrine system and sugar metabolism may be beneficial. If they are muscle sore, natural anti-inflammatory products, such as FRE liquid, prove to be very helpful and avoid the GI toxicity of the drugs often used.
This tip was brought to you by KAM Animal Services, home of KAM’s “Equine Learning Circle” FREE webinars, which will take place twice a month. Go to www.kamanimalservices.com to sign up for their next webinar. These webinars will conclude with a question and answer session, so be ready with your nutrition questions.