Diet and conditioning influence bone development

Die and exercise are two manageable factors that may affect bone density an d strength. We proposed that bone density would be affected by a 12-week co urse of physical conditioning, and by dietary Ca concentration and dietary cation-anion difference (DCAD). Twelve initially unconditioned Arabian hors es were conditioned for 12 weeks on high-speed treadmill. Diets were design ated HH (high Ca, high Cl), HL (high Ca, low Cl), LH (low Co, high Cl), and LL (low Ca, low Cl). Data were collected from horses at rest every 21 days . Serum or plasma were analyzed for total Ca, Cl, parathyroid hormone (PTH) , hydroxyproline, and osteocalcin. Bone mineral content (BMC) of the left t hird metacarpal bone was estimated by radiographic photometry using an alum inum stepwedge and imaging software. During training, BMC increased by appr oximately 1.0g/cm(2) (about 5%) at 12 weeks in horses fed high Ca diets, bu t not low Ca diets. No difference in BMC was associated with DCAD. Serum Ca and plasma Cl concentrations decreased, and serum PTH concentration increa sed with training. Plasma hydroxyproline was unchanged in horses fed the lo w Ca diets but decreased in horses fed the high Ca diets. Serum osteocalcin increased then decreased with training. The collective results suggest tha t the increase in BMC probably involved bone remodeling. Increased BMC shou ld confer greater strength and reduce the risk of skeletal injuries.