The effect of level of calcium intake on the utilization of phosphorus by the pre-ruminant lamb

Abstract

Four groups of lambs received liquid diets providing 50, 250, 450, and 650 mg calcium/kg liveweight/day between 5 and 70 days of age. Phosphorus balance measurements were made during two 32-day periods to determine the retention and apparent availability of phosphorus. Retention was also estimated by the comparative slaughter technique. The apparent absorption of phosphorus/kg liveweight was similar at all levels of calcium intake in the first period, but was reduced at the two higher levels of calcium intake in the second period. Mean apparent availability of phosphorus was 96 %for the lower level of calcium intake and 86% for the highest level in the first period. The corresponding values in the second period were 90 and 64%. The faecal excretion of phosphorus (mg/kg liveweight) was positively related to the level of calcium intake and was also greater, at each level of calcium intake, forthe older lambs. The excretion of phosphorus in the urine (mg/kg liveweight) was inversely related to the level of calcium intake and was reduced in the older lambs. The retention of phosphorus/kg liveweight gain increased as the level of calcium intake was raised. These results, calculated from the balance studies, were supported by the slaughter analyses.