Mineral nutrition in resting and exercising horses

Abstract

Copper balance was examined in Miniature Horses fed diets containing 12 ppm copper and 73, 170, 400 or 580 ppm zinc in a 4X4 Latin square experiment. Horses were placed in wood metabolism stalls during the last four d of each experimental period for total fecal and urine collections. Copper absorption did not change as zinc intake increased, ranging from 42.2% to 50.7% of intake. Two experiments were conducted to quantify mineral losses in exercising horses. In the first experiment, four Miniature Horses were fed diets consisting of oats and Bermudagrass hay. During the first experimental period, horses were maintained at rest and were placed in wooden metabolism stalls for total collections during the last four d. During the second period, horses were galloped 6.1 km daily. Horses were again maintained in metabolism stalls during the last four d for total collections. Sweat loss was quantified and samples were collected. As intake increased with exercise, fecal excretion of minerals increased, and urinary excretion of sodium, calcium, potassium and chloride decreased, possibly to compensate for minerals lost in sweat. Dietary calcium and phosphorus was adequate to meet the needs of exercising horses, but sodium, potassium and chloride supplementation was indicated. In the next experiment, eight Thoroughbred horses were used in a replicated 4X4 Latin square experiment to verify previous results and to examine effects of feeding a fat-supplemented diet on electrolyte balance. Rations contained electrolyte concentrations as indicated from the previous study. Horses were exercised at two workloads to increase energy requirements approximately 150% and 200%. During the last 4 d of each period, horses were housed in metabolism crates for total collections. Sweat loss was quantified and samples were collected. There were no demonstrated effects on electrolyte balance in horses consuming a fat-supplemented versus a conventional ration. Horses were in near electrolyte balance when fed the concentrations of electrolytes as determined in the previous study. This study indicates that to maintain exercising horses in electrolyte balance, diets should contain 1.3 g sodium, 3.1 g chloride, and 4.5 g potassium/Mcal DE.