Effects of a 61.7 km ride on magnesium and calcium homeostasis in well trained endurance horses

The adequacy of the dietary supply of Mg and Ca was evaluated in seven well trained endurance horses completing a 61.7 km ride. The horses received excessive amounts of dietary magnesium before and during the ride. Blood samples were taken one hour before the start, at the first and second veterinary gate, directly and 1 and 2 hours after the finish. The mean body weight loss was 20.1 ± 3.9 kg which implied a body weight reduction of 4.6 ± 1.0%. No major downward changes of the concentrations of the total and ionized concentrations of calcium and magnesium and erythrocyte Mg concentrations were observed during the ride in response to the Mg and Ca loss via sweat. Also the concentrations of parathyroid hormone and 1,25-dihydroxyvitamin D were not increased. These results demonstrate that under the conditions of this study sufficient amounts of Mg and Ca were available from the diet, from additional supplementation during the ride and from body stores.