A comparison of the effects of porcine somatotropin, genetic selection and sex on performance, carcase and meat quality traits of pigs fed ad libitum

Abstract

A comparison was made of the effect of recombinant porcine somatotropin (PST) and genetic selection on performance, carcase and meat quality traits of entire male and female pigs grown from 50 kg to 90 kg liveweight and fed ad libitum. Pigs of each sex were drawn from a selected and an unselected control line of common genetic origin and subjected to daily intramuscular injections of either 90 g PST or saline per kg body weight. The selected line had undergone a period of selection for low backfat (P2) depth and high growth rate. The effects of PST and selection were additive for all traits. For performance traits, growth rate was increased 17% by PST and 22% by selection, food conversion ratio was reduced 20% by PST and 14% by selection. For carcase traits P2 fat depth was reduced 15% by PST and 14% by selection. Both PST and selection caused a 1.3% reduction in killing out. For chemical composition of soft tissue, fat was reduced 9.1% by PST and 2.4% by selection, water was increased 6.9% by PST and 2.2% by selection, and protein was increased 2.1% by PST. For lean quality traits, PST had the slightly adverse effect of increasing paleness, cooking loss and firmness of certain muscles, particularly in males, but selection had no adverse effect. The changes brought about by PST could be accounted for by the repartitioning of metabolisable energy away from fat and toward protein whereas both repartitioning and increased appetite accounted for the effects of selection.