Mineral balance in juvenile horses in race training

Abstract

This study was conducted to further elucidate the requirements for Ca, P and Mg during exercise induced skeletal modeling and remodeling in juvenile racehorses. Nineteen long yearlings were fed rations containing differing amounts of Ca, P and Mg. Total collections of feces and urine were performed on days 0, 64 and 128 of the trial, and mineral absorption and retention were determined. The horses were maintained in a typical race training protocol to mimic the nutritional stresses placed on long yearlings during strenuous exercise. Calcium absorption and retention were lower (P < .05) at d 64 than d 0 and d 128. However, the efficiency of retaining absorbed Ca was higher at d 64 than d 128. Thus lower calcium retention at d 64 was due to reduced absorption. At d 64, Ca absorption and Ca retention were not maximized at Ca intake of 160 mg/kg/d. At d 128, calcium absorption was maximal at a daily intake of 124.2 mg/kg/d and retention was maximal at a daily intake of 122.7 mg/kg/d. These are 38% and 36% over current NRC (1989) recommendations respectively. Phosphorus absorption and retention were not maximized at the highest intakes fed (66 mg/kg/d) which is 32% over current NRC (1989) recommendations. Phosphorus absorption was reduced at d 64. Urinary excretion of P was least at d 128, but P retention values did not reach d 0 values by d 128. There was a trend for reduced Mg absorption at d 64, and Mg retention was significantly reduced at d 64. At d 64, Mg retention was maximized at a daily intake of 35.6 mg/kg/d which is 66% over NRC (1989) recommendations. The intake of Mg and the efficiency of Mg retention was increased from d 64 to 128, but Mg retention was not maximized even at the highest daily intake of Mg (44 mg/kg/d), over two times the current NRC (1989) recommendations. These data verify that early race training affects the dietary requirements for Ca, P and Mg. More research is needed to define these requirements exactly.