THE SELECTION OF PROTEIN-INTAKE BY PIGS TREATED WITH PORCINE SOMATOTROPIN

The hypothesis that pigs can select a protein intake to meet their lea n growth requirement when given a choice of two diets, differing in pr otein content, was tested in this study. Seventy-two gilts (PIG Cambor ough x Canabrid), of an average initial body weight of 20 kg, were all otted to one of four pens with half-slatted concrete floors and two el ectronic feeders. Two pens of pigs were assigned to a choice-feeding s ystem (choice) and two pens to a single-feeding system (single). Half of the pigs in each pen received a daily injection of 100 mu g/kg BW o f porcine somatotropin (ST) and the other half received a daily inject ion of saline. Feed intake of individual pigs was recorded on a daily basis with the Feed Intake Recording Equipment (FIRE) system. Pigs ass igned to the choice-feeding system were given two feeds of different p rotein content, 10 or 24%, but with similar digestible energy content (13.7 MJ of DE/kg). The single diet contained 16% CP during the grower period and 14% throughout the finisher period. Overall weight gain of pigs was not affected by feeding system or ST injection; however, fee d intake was decreased by injection of ST (P = .006) and by choice fee ding(P = .005). Choice-fed pigs showed decreased dietary protein intak e compared with single-fed pigs. The increased deposition rate of lean and protein with injection of ST did not stimulate an increase in pro tein consumption. Choice feeding and ST injection lowered the amount o f feed or protein required per unit gain, or per unit of lean or prote in deposited. Injection of ST significantly decreased the amount of fa t and increased the lean and bone content of the wholesale prime cuts. Choice feeding and ST injection resulted in a decrease (P = .001 to . 09) in backfat thickness. There was a significant increase in protein and unsaturated fatty acid (UFA) and a decrease in DM, crude fat, and saturated fatty acid (SFA) content in lean tissue of ST-treated pigs. Choice feeding resulted in (P = .004) a decrease in UFA and an increas e of SFA. Injection of ST increased plasma urea nitrogen, GH, IGF-I, a nd insulin concentration and decreased plasma glycerol concentration. The deposition rates of lean, fat, and bone were not affected by choic e feeding. Injection of ST increased (P = .003 to .001) the deposition rates of lean, bone, and protein and decreased (P = .001) the deposit ion rate of fat tissue.