Conceptus and maternal responses to increased feed intake during early gestation in pigs

Maternal diet influences fetal growth and postnatal development. We hypothesized that conceptuses gestated in sows provided ad libitum vs. restricted feed intake would differ in the milieu of hormones, growth factors, nutrients, and metabolites associated with growth and metabolism. This hypothesis was tested in two experiments by providing fourth-parity sows (Pig Improvement Co. C15 bred to Line 326 boars) with either 1.81 kg/d (as-fed basis; control) or ad libitum access to gestation diet. In Exp. 1, control (n = 6) or ad libitum (6.4 +/- 0.11 kg/d; n = 9) treatments were provided from d 29 to 45 (onset of estrus is d 0), and sows were slaughtered on d 46. Ad libitum sows gained more weight from d 29 to 45 than controls (34.0 vs. 4.32 kg, respectively; P < 0.01). No differences were observed on d 46 for the number of fetuses, conceptus attachment length, allantoic + amniotic fluid volume, placental weight, fetal weight, and fetal crown-to-rump length. Variation in fetal crown-to-rump length was less (P < 0.03) in sows fed ad libitum. Sows fed ad libitum had greater (P < 0.01) IGF-I and insulin concentrations in plasma than controls on d 43. In Exp. 2, sows were fed 1.81 kg/d (n = 6) or ad libitum (7.0 +/- 0.11 kg/d; n = 4) from d 30 to 56 of gestation, when sows were anesthetized and samples were collected surgically from their gravid uteri. Sows fed ad libitum gained more weight (P < 0.01) than did controls and had more (P < 0.06) IGF-I in their plasma and the plasma collected from umbilical veins of their fetuses. No differences were found for concentrations of insulin or glucose in plasma of sows or fetuses, but urea N concentrations were greater (P < 0.05) in maternal plasma and in the plasma, and allantoic and amniotic fluids of conceptuses from sows fed ad libitum. Combined data from Exp. 1 and 2 revealed a treatment x fetal number interaction (P < 0.05) for average fetal weight. The expected negative relationship between within-litter average fetal weight and the number of fetuses per uterus was observed for control sows (y = 115.4 -1.75 x fetal number; P < 0.05), but litters of ad libitum sows did not show this effect. The hypothesis that providing feed in excess of established requirements in early gestation affects the in utero milieu is supported by these results. Data further reveal that, at least at mid-gestation, the restraint to fetal growth that is exhibited when fetal number increases in control sows is not exhibited when sows are fed ad libitum.