Effects of overfeeding naturally-mated adolescent ewes on maternal, fetal, and postnatal lamb growth.

The objective of this study was to evaluate the effects of overfeeding naturally-mated adolescent ewes (Ovis aries) on maternal, fetal, and postnatal lamb growth, hormone concentrations, and lamb carcass characteristics. Two experiments were conducted in which singleton-bearing adolescent ewes were fed a diet containing 2.72 Mcal/kg ME at a rate which met NRC gestational age requirements (MN; n = 10 in Exp. 1, n = 7 in Exp. 2) or were fed the same diet ad libitum (15% refusal rate) throughout gestation (HN; n = 7 in Exp. 1, n = 6 in Exp. 2). Ewe BW was greater (P < 0.05) for HN than MN ewes beginning on 75 d and 52 d of gestation for Exp. 1 and 2, respectively. Final BCS was greater (P ≤ 0.05) for HN than MN ewes in both experiments; 3.5 vs. 3.0, respectively, for Exp. 1, and 4.8 vs. 2.9, respectively, for Exp. 2. Fasting maternal blood insulin concentrations were greater (P ≤ 0.05) in HN ewes near term (135 d of gestation), whereas fasting maternal glucose concentrations were greater (P ≤ 0.05) during most of the second half of gestation in HN ewes, for both experiments. Gestation length did not differ (P = 0.69) between treatments in Exp. 1, but in Exp. 2, HN ewes had shorter (P = 0.01) gestation lengths (144 vs. 149 d) and had increased (P = 0.002) dystocia scores. Fetal abdominal circumference was greater (P < 0.05) in lambs from MN than HN ewes at 97 d of gestation in Exp. 1 (20.8 vs. 17.4 cm) but did not differ (P = 0.94) between treatments at 95 d of gestation in Exp. 2 (averaging 20.5 cm). There were no differences (P ≥ 0.15) in lamb BW, abdominal circumference, crown-rump length, and biparietal distance at birth; or in postnatal BW and plasma concentrations of glucose, insulin, and lactate in either experiment. There were no differences (P ≥ 0.18) in HCW, dressing percentage, LM area, fat thickness, or KPH between treatments in Exp. 2. Although there was no difference (P ≥ 0.31) between treatments in concentrations of IGF1 or IGF2 mRNA in liver samples collected at harvest, lambs from MN ewes had greater (P ≤ 0.05) concentrations of IGF1R and INSR mRNA, suggesting long-term effects of maternal diet on postnatal hepatic function. In conclusion, excess nutrition during gestation in naturally-mated adolescent ewes did not affect birth weight or postnatal performance of offspring.