Abstract
This experiment investigated the impacts of heavier live weight of twin-born ewe lambs at mating on reproductive performance. Romney ewe lambs (n=270) were allocated to one of two groups: 'Heavy' (48.0±3.8 kg), had been preferentially fed from weaning to breeding, or 'Control' (44.8±3.5 kg). Both groups were exposed to crayon-harnessed vasectomised rams for 68 days before breeding, and then were bred to entire Romney rams for 34 days. Crayon marks were recorded every 17 days. Heavy ewe lambs were more likely to be mated in the first 17 days of breeding (69.9% vs. 54.8%, P<0.05), mated in the entire breeding period (85.1% vs. 69.4%, P<0.01) and had a greater litter size (0.99 vs. 0.65; P<0.01) than did Control ewe lambs. Heavier live weight at mating improved reproductive performance of ewe lambs. These results emphasise the importance of an adequate live weight at breeding for reproductive success in ewe lambs.