Recurrent exertional rhabdomyolysis (RER, a type of tying-up) is an inherited disorder in Thoroughbreds. Research suggests that RER involves an abnormality in the regulation of calcium in muscle cells. High-grain diets have been implicated as triggers of acute episodes, perhaps because of their influence on calcium balance.

Research in cattle has shown that electrolytes and minerals, such as calcium, can be manipulated by altering the dietary cation-anion balance (DCAB). Cations (sodium, potassium) and anions (chloride, sulfur) can be added to or subtracted from the diet to alter concentrations of other compounds. High-grain diets typically have a low DCAB, but it’s not known if this feature alone can trigger attacks. If it can, are only RER horses susceptible, or normal horses, too? To investigate this further, Minnesota, Kentucky, and California researchers collaborated on a study to determine whether electrolyte and mineral concentrations in the blood differ in horses with RER versus normal horses fed diets of low, medium, or high DCAB.

The results showed no difference in the responses of RER and normal horses to changing DCAB. The different diets did affect certain plasma and urine characteristics, but these were seen in all horses. Importantly, the daily balance (retention in the body), of calcium, phosphorus, sodium, chloride, and potassium didn’t change among the different horses. This led the authors to conclude that while DCAB can alter electrolyte and mineral balances, there is no evidence that RER horses respond differently than normal horses. In addition, it is likely that RER involves more than simple calcium imbalance in the diet.

McKenzie, E.C.; Valberg, S.J; Godden, S.M.; et al. American Journal of Veterinary Research, 63(7): 1053-1060, 2002