EFFECTS OF SOMATOTROPIN AND SALBUTAMOL IN 3 GENOTYPES OF FINISHING BARROWS - GROWTH, CARCASS, AND CALORIMETER CRITERIA

We evaluated the combined use of 0 or 4 mg/d of recombinant porcine so matotropin (pST) and 0 or 2.75 ppm salbutamol in three genotypes of gr owing barrows (139 d old) differing in lean and lipid accretion potent ial. Treatments were in a 2 x 2 x 3 factorial arrangement, and the thr ee genotypes tested were Meishan (M, n = 32, 49 kg), Duroc x White com posite (D x Wc, n = 31, 62 kg), and Meishan x White composite (M x Wc, n = 31, 64 kg) pigs. Growth performance was evaluated over 28 d for i ndividual pigs, and 20-h feed-deprived heat production was measured be fore slaughter (d 34). Daily pST injection increased ADG (+70 g/d) and reduced ADFI (-.61 kg/d) across genotypes (P < .05). Salbutamol incre ased (P < .05) ADG in M x Wc pigs (+146 g/d) but not in M pigs (-60 g/ d) or D x We (+80 g/d) pigs. However, M pigs had the lowest ADG and AD FI, and M x We pigs not treated with salbutamol grew slower than D x W e pigs (P < .05). Carcass protein and moisture accretion were additive ly (P < .05) increased by pST and salbutamol for D x We and M x Wc pig s. Meishan pigs had increased carcass protein and moisture accretion f rom pST, whereas only moisture accretion was increased by salbutamol ( P < .05). The longissimus muscle area and semitendinosus weight increa sed as the percentage of M in the genotype decreased (P < .05), and bo th were increased by pST or salbutamol treatment (P < .001). Leaf fat was decreased more (P < .05) in M pigs than in D x Wc or M x Wc pigs w ith pST injection. The similar magnitude of leaf fat reduction between D x Wc and M x Wc pigs resulted in a mean genotype difference (P < .0 5), and salbutamol decreased leaf fat across genotypes. Oxygen consump tion and heat production were increased by pST in M pigs more than in the crossbred genotypes, but CO2 production was reduced by similar mag nitudes across genotypes, and salbutamol only tended to reduce CO2 pro duction in D x Wc pigs. In general, these data indicate that pST and s albutamol result in additive increases in carcass lean composition; ho wever, growth rate, carcass accretion, and various organ weights may v ary among genotypes with salbutamol and pST treatment.