Effects of exogenous somatotropin during early gestation on maternal performance, fetal growth, and compositional traits in pigs

The objective of this study was to determine the effects of maternal treatm ent with porcine somatotropin (pST) during early gestation on embryonic sur vival, fetal development, and internal environment for fetal growth. Sixty- two crossbred gilts received daily injections of either 3 mt of a placebo ( control, n = 31) or 6 mg of pST (n = 3 1) from d 10 to 27 of gestation. Rep resentative gilts were slaughtered on d 28, 37, and 62 of gestation. The re maining gilts were allowed to farrow. It was found that embryonic survival was not influenced by pST treatment (P > 0.10). However, pST affected the g rowth and composition of the maternal (endometrium) and fetal (chorion) par ts of the placenta. Thus, endometrial RNA concentration tended to be increa sed by pST at d 37 (P = 0.15), and it was increased at d 62 (P < 0.05) of g estation, which is indicative of increased capacity for protein synthesis. At birth, placental chorion weight (P < 0.10) and contents of DM and protei n (P < 0.05) were increased due to PST treatment, but no effects were detec table up to d 62 of gestation. Maternal pST treatment was effective at incr easing nutrient supply to the embryo as suggested from elevated glucose con centrations in amniotic and allantoic fluids (P < 0.05) at d 28 of gestatio n. With regard to prenatal growth, embryonic DNA concentration was slightly elevated at d 28 (P < 0.10), but pST did not induce any changes in average embryonic, fetal, or neonatal weights. However, within litters, the birth weights of piglets in the 25% lowest weight group (LW) were increased by PS T treatment vs control LW pigs (1,241 + 55 vs 1,099 +/- 59 g, P < 0.10). Th irty-eight neonates from 15 litters divided among the three weight groups w ere examined for body composition. The weight of the intestinal tract was i ncreased above average after maternal pST treatment (P < 0.01). Additionall y, the amounts of tissues such as bone (P = 0.12) and s.c. fat (P = 0.06), and of protein, fat (P = 0.10), and ash (P < 0.05) were increased, whereas the relative body composition remained unchanged by pST (P > 0.10). On aver age, muscle protein concentration was elevated due to PST (P < 0.01), and, in LW piglets, plasma IGF-I concentration was increased (P < 0.10). The res ults suggest that maternal somatotropin is a critical factor in early pregn ancy capable of influencing placental nutrient transfer and placental growt h. It thereby selectively improves the growth conditions for the smaller li ttermates.