Bone density and geometry in juvenile racehorses fed differing amounts of minerals

Abstract

This study was conducted to further elucidate the mineral requirements of the juvenile horse in training. Horses were fed rations containing differing amounts of calcium, phosphorus and magnesium and in reference to mineral intake, groups were designed as low, moderate, moderately high and high. Radiographs of the third metacarpal (MCIII) were taken on day 0, 28, 60, 92 and 124 to evaluate change in bone density and bone geometry. Bone density was expressed as radiographic bone aluminum equivalence (RBAE) and bone geometry was expressed as the width in millimeters (mm) for particular aspects of the bone. Total RBAE increased in all horses during the first sixty days. Change in total RBAE in horses consuming moderately high and high mineral intakes were significantly higher than in horses consuming moderate and low mineral intakes. Demineralization of the dorsal and palmer cortices in the first half of the study was not as prominent in horses consuming the high and moderate high mineral intakes compared to those consuming the moderate and low mineral intake groups. Total bone width tended to increase in the first sixty days, then increased significantly in the last sixty days of the study. No effects of mineral intake were seen in the total bone width or in any other geometric measurements. As a function of total bone, the medullary cavity decreased throughout the study probably due to endosteal bone remodeling of the dorsal cortex. Dorsal bone growth was significant throughout the study, but there were no effects of mineral level intake on changing dorsal cortical width. While higher mineral intakes appeared to have protective effects on the density of the dorsal and palmer cortices, these changes were not reflected in greater bone size. High mineral intakes produced significantly higher RBAE values in the first 60 days while geometric measurements were not significantly different between the four mineral groups. Since the low and moderate mineral intake groups experienced significantly more demineralization early in training without loss in bone size, it is suggested that the bone may have become weaker. The possibility of lessening bone related injuries from the time period during bone demineralization by a protective effect of higher mineral intake warrants further investigation to better define the mineral requirements of the juvenile horse in training.