Tying up, or exertional rhabdomyolysis (ER), is an exercise-induced syndrome of muscle pain and cramping. Classic signs of ER include muscle pain and stiffness, excessive sweating, and reluctance to move. Researchers have uncovered several different causes for ER, including nutrition, over-exertion and genetics.
The two main chronic forms are recurrent exertional rhabdomyolysis (RER) and equine polysaccharide storage myopathy (EPSM). Horses may experience a single, acute episode of ER although they likely do not have the same muscle defects as RER or EPSM.
Sugar stored in the muscle is known as glycogen. Normally, glycogen is broken down by an enzyme known as amylase and used as energy for performance. Horses with EPSM cannot metabolize glycogen normally. The muscle therefore can’t use glycogen for energy, and glycogen stores build up abnormally. Symptoms include those associated with ER, but may include exercise intolerance, muscle stiffness, back pain, shifting lameness, muscle atrophy, and a camped-out stance.
Dietary Goals for EPSM or RER horses
|Good Quality Hay||Provide 1.5-2% of body weight per day|
|Pasture||Restrict access w/grazing muzzle esp. with rich pasture|
|% Digestible Energy as NSC||<15% NSC||<20% NSC but not < 10% for horses in intense work|
|% Digestible Energy as Fat||5-10% fat||15-20% fat|
Both hot and humid conditions and over-exertion can cause acute sporadic ER episodes. In the cases of dehydration, an electrolyte, along with adequate water, can be used to replenish electrolytes lost in sweat.
Dietary management includes keeping starch and sugar in the total diet to less than 20% for RER horses1, 10-12% or less for PSSM horses2,3. Exercise should be introduced slowly, with changes and increases in intensity made gradually. Stress in the environment should be kept to a minimum.
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