The effect of calcium and phosphorus supplementation, inactivity, and subsequent aerobic training on the mineral balance in young, mature, and aged horses

A randomized complete block design experiment was conducted to determine the effect of Ca and P supplementation, inactivity, and subsequent aerobic exercise on Ca and P serum concentrations, and balance and digestibilities in young, mature, and aged horses. Twelve stock-type geldings were blocked into three age groups: 2 and 3, 7 to 11, and 15 to 21 years of age. Two groups of six horses were randomly assigned to either control (C) or mineral supplemented (T) diet. Horses consuming C received about 133% of National Research Council (NRC) requirements for Ca and P, while horses consuming T received about 275% of NRC requirements for Ca and P. The trial consisted of eight 21-d periods. During periods I, II, and III, all horses were inactive, and during periods IV, V, VI, VII, and VIII, all horses performed an ascending aerobic exercise regimen. Serum samples were taken at the beginning of period I and at 21-d intervals thereafter for determination of serum Ca and P. Total fecal and urine collections were taken for 72 h at the beginning of period I and at 21-d intervals thereafter for determination of Ca and P balance. Overall mean apparent Ca balance was affected by treatment (P < .009); time (P < .001); and the interaction of time and treatment (P < .001). Overall mean apparent Ca balance was higher (P < .009) for T as compared to C (23.63 vs. 3.77 mg/kg BW). Mean apparent Ca digestibility was affected by time (P < .001) and the interaction of time and age (P < .001). Mean apparent P balance was affected by time (P < .001) and the interaction of time and treatment (P < .032). Increases in Ca balance may indicate more available mineral for bone metabolism, particularly when remodeling is triggered with the onset of exercise following a sedentary period, suggesting a possible benefit to feeding additional Ca above current NRC recommendations.