Growth, body composition, and endocrine responses to chronic administration of insulin-like growth factor I and(or) porcine growth hormone in pigs.

The actions of IGF-I, alone and in combination with porcine growth hormone (pGH), on growth and circulating endocrines and metabolites important in growth were investigated in peripubertal-age Meishan barrows. Pigs were assigned to four treatments: control, buffer; IGF-I, 33 microg rhIGF-I/kg BW injected twice daily; pGH, 33 microg rpGH/kg BW injected once daily; and IGF-I+pGH, 33 microg rhIGF-I/kg BW injected twice daily plus 33 microg rpGH/kg BW injected once daily. Treatments were administered for 28 d. Feed intake, BW, and backfat were recorded and blood samples were collected weekly. At slaughter, organ and primal cut weights were recorded. Offal and half the carcass were ground for chemical analysis. Serum concentrations of IGF-I on d 7, 14, 21, and 28 in the IGF-I, pGH, and IGF-I+pGH groups were increased 60, 107, and 131%, respectively, compared with those of the control group. Administration of pGH increased gain 43%, feed efficiency 60%, carcass protein accretion 88%, and trimmed lean cuts 16%, whereas IGF-I administration increased gain 22%, carcass protein accretion 33%, and trimmed lean cuts 5%. There was little difference in responses to administration of IGF-I+pGH and pGH alone except that coadministration of IGF-I with pGH reduced the ability of pGH to suppress backfat gain (P < .02). Even though administration of IGF-I resulted in a 60% increase in chronic nadir serum concentrations of IGF-I, only a few growth and carcass measures were changed when compared with control pigs. These included increased (P < .05) weight of body, leaf fat, kidneys, and belly. The actions of pGH on growth of pigs were not mimicked, and some were countermanded by administration of IGF-I at a dose that produces significantly increased serum concentrations of IGF-I.