Calcium Level for Developing Boars and Gilts

Abstract

Seventy-two animals were utilized in two experiments to study the calcium requirement of developing boars and gilts. In experiment 1, 12 boars and 12 gilts were randomly assigned in a 2 × 3 × 2 factorial arrangement to dietary calcium levels of 0.6, 0.9 and 1.2% of the diet with replication. Dietary phosphorus was maintained at 0.5%. Boars had less backfat, were longer and had smaller loin eye areas than the gilts. No other sex or calcium treatment differences in carcass characteristics or ham composition were observed. Increased dietary calcium tended to increase serum calcium and serum alkaline phosphatase activity and decrease serum inorganic phosphorus. Bone weight and strength were decreased by elevated dietary calcium while bone mineral composition was not altered. Boars had significantly heavier bones with higher moments of inertia but had lower breaking stress values than gilts. Neither sex nor dietary calcium level influenced the degree of turbinate atrophy. The amount of cartilage included in the bony matrix was highly correlated with the degree of turbinate atrophy. In experiment 2, 24 boars and 24 gilts were randomly allotted to the same dietary treatments as experiment 1. Boars gained faster and were more efficient in converting food to liveweight gain than gilts, but feed consumption was not different. Phalanx ash and calcium concentrations were higher for the gilts than the boars, and increased dietary calcium tended to increase phalanx calcium concentration. Boars had heavier and stronger bones than the gilts. Bone breaking strength and bending moment were reduced by increased dietary calcium. Turbinate ash and calcium concentrations were higher for boars than gilts. No other sex or treatment differences were observed in turbinate mineral content or histopathology. Under the conditions of this study (0.5% total dietary phosphorus) the calcium requirement of developing boars and gilts is not greater than 0.6% of the diet. Several of the parameters investigated during the trial indicated that the available dietary phosphorus was limiting the expression of any higher requirement for calcium.