Annual lambing performance of crossbred ewes in out-of-season and accelerated lamb production systems

Abstract

The average annual lamb production of 1182 crossbred ewes was evaluated in three lamb production systems over 4 years at two sites (Cowra and Wagga Wagga). The lamb production systems were: accelerated 8-monthly joinings with two flocks joined 4 months apart (Ac8), spring joining with an autumn back-up joining (SpB), and annual autumn joining (AuA). The Ac8 and SpB systems were evaluated at Cowra and the SpB and AuA systems were evaluated at Wagga Wagga. Two genotypes of ewes, Border Leicester × Merino (BLM) and Hyfer (Dorset × Merino composite), were used at both sites, with natural joinings to Dorset, Suffolk or Hyfer rams. Four traits were analysed separately at each site to evaluate the average performance per ewe joined per year: number of lambings, number of lambs born, number of lambs weaned and total weight of lamb weaned. Analyses were also undertaken using only spring joining data. At Cowra ewes in the Ac8 system had more lambings (1.23 vs 0.87), lambs born (1.88 vs 1.28), lambs weaned (1.47 vs 1.00) and weight of lamb weaned (31.1 vs 21.5 kg) than ewes in the SpB system (P < 0.01). At Wagga Wagga the AuA system had significantly more lambs born (1.37 vs 1.13), lambs weaned (1.08 vs 0.95) and weight weaned (26.1 vs 21.9 kg) than the SpB system (P < 0.01). The system × breed interaction was significant for all traits because the BLM ewes were greater than Hyfer ewes in the AuA, but the reverse in the SpB system. At both sites the advantage of the back-up joining over only joining in spring was greater for the BLM than the Hyfer ewes. The relative performance of the various lamb production systems for each ewe breed is presented. An accelerated lambing system is likely to be more successful using ewes that have an extended breeding season and good out-of-season breeding performance.