Effect of weaning age on growth rates of lambs infected by gastrointestinal parasites

Gastrointestinal parasitism is one of the most important challenges facing low chemical or organic livestock production systems but also conventional farmers as resistance to anthelmintics becomes more widespread. Young twin-born and reared lambs were challenged for 5 days (Experiment 1) or trickle infected with parasites (Experiment 2) and not weaned (Expt. 1. only) or early (8 and 7 weeks) or late weaned (16 and 14 weeks; Expt. 1 & 2 respectively). Liveweight gain was measured until lambs were 19 weeks of age (Expt. 1) or 25 weeks of age (Expt. 2). Early weaning (7-8 weeks) reduced liveweight gain by at least 25% in both years and lambs remained 5 kg lighter at the completion of the experiments. Parasite infection had modest effects on lamb performance and there was no interaction between weaning age and parasite infection in either year. Infected lambs generally grew well, gaining at least 90 g/d possibly due to the relatively young age of the lambs limiting their ability to mount an immune response.