The effect of calcium and phosphorus supplementation on bone metabolism inyoung, mature, and aged horses during inactivity and subsequent aerobic training

An experiment was performed to determine the effects of Ca and P supplement ation, inactivity, and subsequent aerobic exercise on bone metabolism in yo ung, mature, and aged horses. Twelve stock-type geldings were blocked into three groups: 2 and 3, 7 to 11, and 15 to 21 years of age. Horses within ag e groups were evenly divided and randomly assigned to one of two dietary tr eatments; control (C) or Ca and P supplementation (T). Horses consuming C a nd T received about 133% and 275% of National Research Council (NRC) requir ements for Ca and P, respectively. The trial consisted of eight 21-day peri ods. During periods I, II, and III, all horses were inactive and received n o forced exercise. During periods IV, V, VI, VII, and VIII, all horses were placed on an ascending aerobic exercise regimen. Blood samples were taken at the beginning of period I and at 21-day intervals thereafter to determin e serum concentrations of osteocalcin (OST) and type I carboxyterminal telo peptide (ICTP). Dorsal-palmar and lateral-medial radiographs were taken of the left third metacarpal at the beginning of period I and at 21-day interv als thereafter to monitor changes in bone densities, as indicated by radiog raphic bone aluminum equivalencies (RBAE). Mean serum OST was affected by age (P < .004) and the interaction of time a nd age (P < .006). Mean serum ICTP was affected by age (P < .001), time (P < .001), the interaction of time and age (P < .001); and the interaction of time and treatment (P < .05). There was an effect of treatment on overall mean medial (MRBAE; P < .04) and total (TRBAE; P < .04) RBAE. Overall mean dorsal RBAE (DRBAE; P < .001), palmar RBAE (PRBAE; P < .003), lateral RBAE (LRBAE; P < .001), MRBAE(P < .001), normalized MRBAE (P < .001), TRBAE (P < .05), and normalized TRBAE (P < .05) were affected by time. There was an e ffect of the interaction of time and age on overall mean DRBAE (P < .05), L RBAE (P < .002), MRBAE (P < .02), normalized MRBAE (P < .02), TRBAE (P < .0 05), and normalized TRBAE (P < .005). Overall mean DRBAE (P < .02) and PRBA E (P < .001) were affected by the interaction of time, treatment, and age. Biochemical and radiographic data from this experiment indicate that dietar y Ca and P supplementation may affect bone remodeling in aerobically exerci sed horses of varying ages following a period of inactivity. Furthermore, t he data indicate that bone in horses of varying ages responds differently t o inactivity and exercise.