CHARACTERIZATION OF CHANGES RELATED TO MINERAL BALANCE AND BONE METABOLISM IN THE YOUNG RACING QUARTER HORSE

This study was conducted to determine physiologic responses reflective of bone metabolism during the onset of training and to relate those r esponses to the mineral requirements of young racehorses, Ten previous ly untrained Quarter Horse geldings were put into race training. They were fed a diet balanced to meet NRC recommendations for young horses in training. Feed, feces and urine were collected, weighed and analyze d over the experiment to determine mineral balance. Radiographs were t aken of the left front leg to determine mineral content of a cross-sec tional area of the third metacarpal. Blood samples were taken to deter mine osteocalcin, parathyroid hormone, 25-hydroxyvitamin D, Ca and ino rganic P concentrations. Horses were gentled to ride, trained to gallo p on the track and maintained in training for four 28-day periods. Blo od serum was collected every 14 day, while radiographs and 72-hr total collections of urine and feces were taken every 28 d. Radiographs dem onstrated that mineral content was lowest at day 56 in the dorsal, pal mar and medial cortices of the third metacarpal. Urinary Ca declined d ramatically from day 0 to day 28, then remained constant to day 56, be fore decreasing at day 84, Fecal Ca peaked at day 28 and remained elev ated above day 0 amounts until day 112. Calcium retention was negative at day 0, became slightly positive by day 28 and increased through da y 112. Phosphorus and Mg balance remained relatively unchanged through out the duration of the study. This study demonstrated changes in the mineral content of the third metacarpal and Ca balance during early tr aining and suggests that further studies be performed.