Moderate doses of porcine somatotropin do not increase plasma insulin-likegrowth factor-I (IGF-I) or IGF binding protein-3

The growth rate of the young pig is generally much less than its potential and may be constrained by endocrine status as well as by nutrient intake. T he aim of this study was to determine whether porcine somatotropin (pST) co uld increase growth in the nursing pig. Fourteen sows nursing litters of 6 (n = 7) or 12 (n = 7) piglets were utilized to establish a high and low pla ne of nutrition for sucking pigs. On Day 4 of lactation, the median two mal e pigs from each litter were randomly allocated to one of two doses of PST (0 or 60 mu g/kg/d) until weaning on Day 31. Pigs were bled on Days 4, 13, 22, and 31 of lactation and the plasma was analyzed for insulin-like growth factor (IGF)-I, IGF-II, and IGF binding protein-3 (IGFBP-3). Pigs were wea ned into conventional accommodation and further weighed on Days 63, 91, and 119. Pigs from litters of 6 grew more quickly and weighed 2.2 kg (P = 0.01 ) and 3.5 kg (P = 0.04) more than pigs from litters of 12 at 31 and 63 d of age, respectively. There was no effect of pST on preweaning growth of suck ing pigs (261 vs. 258 g/d, P = 0.68), although growth rate increased in the final 3 d before weaning at 31 d (241 vs. 294 g/d, P = 0.01). IGFBP-3 was greater (1.09 vs. 0.78 mu g/ml, P < 0.001), whereas IGF-I tended to be grea ter (206 vs. 176 ng/ml, P = 0.14), in pigs from the small litters. There wa s no effect of PST on plasma IGF-I (182 vs. 195 ng/ml, P = 0.454) or IGFBP- 3 (0.93 vs. 0.94 mu g/ml, P = 0.85) concentrations. Plasma IGF-I and IGFBP- 3 were highly correlated with the growth rate of nursing pigs (R = 0.638 an d 0.756, respectively). There were no effects of pST (340 vs. 328 ng/ml, P = 0.48) or litter size (336 vs. 333 ng/ml, P = 0.88) on IGF-II. In conclusi on, pST had no little or no effect on growth performance or plasma IGF-I, I GF-II, or IGFBP-3 in sucking pigs on either a high or low plane of nutritio n. (C) Elsevier Science Inc. 1999.