Effects of dam size and nutritional plane during pregnancy on lamb performance to weaning

This study examined the effects of dam size and plane of nutrition during pregnancy on dam udder size, lamb colostrum intake, and lamb liveweight gain (LWG). The study also attempted to quantify the effects of a number of dam and offspring parameters on lamb LWG. Two hundred and fifty-five heavy (H) (60.8±0.18 kg) and 255 light (L) (42.5±0.17 kg) Romney dams were allocated to ad libitum (A) or maintenance (M) nutritional regimens, underNewZealand pastoral grazing conditions – from day 21 to day 140 post-insemination. One week prior to lambing, all dams and offspring were managed as one group and provided with ad libitum feeding. Udder dimensions were measured at day 140 of pregnancy in a subgroup of 313 dams. Lambs were weighed within 24 h of birth (L0) and at L21, L45, L80 and L100 and the lamb liveweight gains calculated. From a sub-group of 167 lambs, blood was sampled at 24–36 h of age to determine the glucose and gamma-glutamyltransferase (GGT) concentrations. During pregnancy, the M-dams gained less live weight than the A-dams and gave birth to lighter lambs – which resulted in a reduced LWG, until L21. From L21 onwards, the LWG of the lambs born to M-dams did not differ from lambs born to A-dams. Udders of the LA-dams were bigger than those of LM-dams. Lambs born to A-dams recorded a higher blood glucose concentration than lambs born to M-dams. Dam size and nutrition did not affect the GGT concentrations of the lamb. Heavy (H) dams remained heavier than the Ldams throughout pregnancy and gave birth to heavier lambs, than the L-dams. Lambs born to H-dams recorded greater LWG than lambs born to L-dams during early, mid and late lactation. Modelling of the results showed that only a small part of the variation (±35%) of LWGof the lambs could be explained by the measured variables (e.g., birth weight, dam live weight, sire, udder dimension, nutrition). The largest single variable explained less than 5% of the variation in LWG. In conclusion, this study showed that lamb liveweight gain in early lactation is affected by both dam size and plane of nutrition and could likely be explained by differences in the lactational performance of the ewes. Interestingly, modelling of the results showed that a considerable proportion of lamb liveweight gain was not explained by the variables measured.