DECONDITIONING REDUCES MINERAL-CONTENT OF THE 3RD METACARPAL BONE IN HORSES

Diet and exercise are two management factors that affect bone density and strength. We proposed that bone density and calcium status would b e affected by deconditioning for 12 wk and by dietary Ca concentration . Eleven highly conditioned Arabian horses were taken out of training and placed in stalls for 12 wk. Horses were walked on a mechanical wal ker in two 30-min sessions, 7 d/wk. Diets were designated CC (.36% Ca) and HC (.62% Ca). Data were collected every 21 d. Serum or plasma wer e analyzed for total and ionized Ca, parathyroid hormone, osteocalcin, hydroxyproline, electrolytes, and blood gases. Bone mineral content ( BMC) of the left third metacarpal bone was estimated by radiographic p hotometry using an aluminum step wedge, which was exposed in each radi ograph, as a reference standard for an image analysis system. During d econditioning, BMC decreased by approximately 1.1 g/2 cm, or.45% per w eek. This decrease was unaffected by dietary Ca. Serum Ca concentratio n increased with deconditioning. The results suggest that dietary Ca a t twice the currently recommended level did not prevent the loss of BM C in response to deconditioning. Loss of BMC during 12 wk of stall con finement may weaken bones, increasing the risk of skeletal injuries wh en training is resumed.