INFLUENCE OF PORCINE SOMATOTROPIN ON THE PHOSPHORUS REQUIREMENT OF FINISHING PIGS - II - CARCASS CHARACTERISTICS, TISSUE ACCRETION RATES, AND CHEMICAL-COMPOSITION OF THE HAM

We investigated the effects of recombinant porcine somatotropin (pST) on the requirement for P to maximize lean tissue accretion and to mini mize fat tissue accretion in two experiments using finishing pigs. Cor n-soybean meal diets with varying levels df P were fed, and Ca was adj usted to maintain a Ca:P ratio of 1.1:1. In Exp. 1, 96 pigs were fed d ietary P concentrations of .35, .45, and .65% from 75 to 109 kg BW. On e-half of the pigs were injected daily with 4 mg of pST. Administratio n of PST increased (P <.05) percentages and accretion rates of lean ti ssue, bone, skin, water, and protein, but it reduced (P < .05) those o f fat tissue and lipid. Increasing dietary P had little effect on chem ical composition or accretion rates in untreated pigs, but it increase d (P <.05) ash percentage and accretion in pigs treated with pST. Expe riment 2 consisted of 66 pigs fed six dietary P concentrations (.35,.5 0,.65,.80,.95, and 1.10%) from 72 to 114 kg. One-half of the pigs were injected daily with 4 mg of pST. Percentages and accretion rates of l ean tissue, bone, skin, water, and protein increased (P <.05) with pST , but those of fat tissue and lipid were reduced (P <.05). Increasing dietary P increased accretion rates of bone and skin (linear, P < .05) , lean tissue, water, protein, and ash (quadratic, P <.05), and it red uced (quadratic, P <.05) that of lipid in pigs treated with pST. Dieta ry P level did not consistently affect percentages or accretion rates of tissues or chemical components in untreated pigs. In most instances , pigs treated with PST required higher dietary P levels and greater d aily intakes of P to maximize lean tissue and protein deposition and t o minimize fat tissue and lipid accretion than untreated pigs. These r esults indicate that finishing pigs treated with pST require higher di etary percentages of P to maximize carcass lean deposition as compared with untreated pigs.