Media Room: Info Sheets

Jun 24th, 2009

Effect of high grain and high NSC horse feed on tying up

What is Tying-up?

Tying-up, otherwise known as exertional rhabdomyolysis, is a term used to describe muscle disorders affecting horses. Horses suffering with tying-up may experience painful muscle contractions, stiffness, profuse sweating, and elevated respiratory rates during or following exercise. There are actually two distinct forms of tying-up, known as polysaccharide storage myopathy (PSSM) and recurrent exertional rhabdomyolysis (RER):

Polysaccharide Storage Myopathy (PSSM)

PSSM is the form of tying-up that affects Quarter Horses and draft breeds. Horses affected by PSSM appear to have an enhanced insulin sensitivity which causes them to store abnormally high levels of glycogen in their muscles. Horses with PSSM appear to have no problem utilising the glycogen they have stored in their muscles when exercising. Why the storage of abnormally high levels of muscle glycogen causes muscle damage is still unknown.

Recurrent Exertional Rhabdomyolysis (RER)

RER is the form of tying-up that commonly affects thoroughbreds. Horses affected by RER do not accumulate high concentrations of muscle glycogen, however they tend to exhibit abnormal muscle contraction mechanisms. RER is often triggered by exercise and excitement.

How is Grain Involved?

The feeding of grain will often increase the occurrence of PSSM and RER in susceptible horses. Grains provide energy in the form of starch (non-structural carbohydrate). Starch is broken down in the small intestine and absorbed into the bloodstream as glucose. For horses affected by PSSM, feeding high starch diets increases the amount of glycogen stored in the muscles, and therefore increases the chances of the disease occurring. For horses with RER, high starch diets often contribute to the horse being highly excitable and nervous, making the horse more susceptible to tying-up. In a nutshell, feeding grain to susceptible horses increases the risk of tying-up occurring.  Low NSC feeds however, such as CoolStance and CoolFibre should not contribute to either kind of Tying Up.