Effect of dietary phosphorus on finishing steer performance, bone status, and carcass maturity

Yearling crossbred steers (n = 60; 386 kg) were individually fed in a compl etely randomized experimental design to determine their P requirement. Trea tments were in a factorial arrangement with two levels of Ca (.35 or .70% o f DM) and five concentrations of P (.14, .19, .24, .29, or .34% of DM). The finishing diet consisted of 34.5% dry-rolled corn, 22.5% brewers grits, 22 .5% corn bran, 7.5% ground corncobs, 5% molasses, 3% fat, and 5% supplement . Supplemental P was provided as monosodium phosphate and Ca as limestone. Ash content was determined on the first phalanx bone from the lower front l egs following slaughter, and rib bone breaking strength was determined with an Instron Universal Testing Machine. Carcass maturity and shear force wer e also evaluated on wholesale rib cuts. Because no interactions between Ca and P levels were detected, only main effects are presented. Daily gain, DM I, and feed efficiency were not affected by dietary P concentration or P in take. Bone ash (g or g/ 100kg BW) and rib bone breaking strength were also unaffected by dietary P. Feeding .7% Ca decreased (P < .06) ADG and efficie ncy compared with feeding .35% Ca. Neither dietary Ca nor P had a significa nt effect on tenderness (shear force), skeletal maturity, or overall maturi ty. These results indicate that the P requirement for finishing yearlings i s .14% of diet DM or less and that supplementing P above levels supplied by basal ingredients in many grain-based finishing diets is not necessary.