Late foetal life nutrient restriction and sire genotype affect postnatal performance of lambs.

This experiment investigates the effects of maternal nutrient restriction in late gestation on the offsprings' postnatal metabolism and performance. Forty purebred Shropshire twin lambs born to ewes fed either a high-nutrition diet (H) (according to standard) or a low-nutrition (L) diet (50% during the last 6 weeks of gestation) were studied from birth until 145 days of age. In each feeding group, two different sires were represented, 'growth' (G) and 'meat' (M), having different breeding indices for the lean : fat ratio. Post partum all ewes were fed the same diet. Lambs born to L-ewes had significantly lower birth weights and pre-weaning growth rates. This was especially pronounced in L-lambs born to the M-ram, which also had markedly lower pre-weaning glucose concentrations than the other three groups of lambs. L-lambs converted milk to live weight with an increased efficiency in week 3 of life. Their glucose concentrations and growth rates were both increased. Plasma glucose concentrations in LM-lambs became similar to those observed in H-lambs post-weaning. However, LM-lambs continued to be lighter than the other groups throughout the experimental period and were unable to compensate for the reduced weight at birth despite having the highest daily fractional growth rates. LG-lambs had the highest plasma glucose concentrations of all four groups of lambs, and they indeed reached body weights comparable to those of the H-lambs by 145 days of age. The increased growth rate post-weaning in L-lambs was not reflected in fat deposition, as L-lambs had lower fat deposition than H-lambs. This may relate to the lower plasma insulin levels found in the L-lambs than in the H-lambs. In conclusion, a 50% reduction of maternal nutrient supply in the last 6 weeks of gestation reduces the birth weight and pre-weaning growth of the offspring due to lower milk intake. Growth rates can be restored when an adequate post-weaning diet is provided, but the prenatal nutrition may programme postnatal metabolism differentially depending on genotype, thus affecting the ability of the ad libitum-fed lamb to achieve a given body weight by a certain age.