Late-pregnancy nutrition differentially affects the birthweight of lambs born to ewes from divergently selected plasma IGF-1 lines

Abstract

Three insulin-like growth factor (IGF-1) sheep genetic selection lines (Low, Control and High) based on phenotypic IGF-1 concentrations post-weaning have previously shown a negative relationship between IGF-1 concentration and lamb birth-weight. The present study was designed to determine if dam nutritional regimen in late pregnancy affected this relationship. Nineteen Low, 66 Control and 51 High IGF-1 selection line pregnant ewes were either offered a restricted or ad-lib nutritional regimen from day 91 of pregnancy. The ewe nutritional regimens resulted in differences (P < 0.05) in ewe liveweight and condition score in late pregnancy. IGF-1 concentrations of High and Low line ewes differed (P < 0.05) throughout the late-pregnancy period with Control line concentrations being intermediate. In late pregnancy, ad-lib ewes had higher (P < 0.05) IGF-1 concentrations than restricted ewes. Neither IGF-1 selection line or nutrition regimen consistently affected ewe glucose, non-esterified fatty acids (NEFA), β-hydroxybuterate or lactate concentrations. Under ad-lib nutritional conditions the birthweights of High line lambs were lighter (P < 0.05) than Control lambs. This relationship was not observed under the restricted nutritional regimen. The interaction between IGF-1 selection line and dam nutrition for lamb birthweight may explain the previously reported variability in the birthweight response between IGF-1 selection lines. We speculate that under conditions of ad-lib dam pregnancy nutrition, High IGF-1 selection line ewes partition resources away from the placenta resulting in poorer foetal nutrition. © 2009 Taylor & Francis Group, LLC.