Horses do not synthesise vitamin D via exposure to sunlight like humans and so they are commonly vitamin D deficient due to inadequate dietary intake. Recent studies have shown that Thoroughbred racehorses are more likely to be deficient in vitamin D due to their limited time at pasture associated with their training and management regime. Vitamin D is essential for normal muscle function and calcium regulation. ‘Tying up’ is a term used to describe Recurrent Exertional Rhabdomyolysis (RER) and is a disease that affects ~6% of racing Thoroughbreds worldwide and results in debilitating muscle pain, cramps and, in severe cases, euthanasia. 

The mechanism behind RER is poorly understood but there is evidence that RER is associated with altered calcium regulation within skeletal muscle.

The aim of this study was to establish whether differences in vitamin D metabolism are evident between horses with RER and control horses.

RER horses were found to have significantly lower levels of the active form of Vitamin D when compared to control horses, therefore supporting our hypothesis that vitamin D metabolism has a role to play in RER.