Productivity of three crossbred ewe types mated naturally at 8-monthly intervals over two years

Abstract

Productivity is reported for 175 Booroola MerinoxPoll Dorset (BD), 288 Trangie Fertility MerinoxPoll Dorset (TD) and 248 Border LeicesterxMerino (BLM) ewes joined three times (February, October and June) in 2 years. Overall joining in February resulted in higher performances (153¦3% lambs born, 118¦3% lambs weaned, 24.7¦0.6 kg weight of lamb weaned, per ewe joined) than were obtained following October and June joinings (129¦4% born, 93¦3% weaned, 15.3¦0.5 kg weight weaned per ewe joined). The mean number of lambings per year was 1.28¦0.02 with an annual lambing rate of 211¦4% lambs born and 160¦3% lambs weaned. For lambs born, BD ewes were consistently higher than the other ewes, with BLM ewes having fewer lambs born from October and June joinings (P < 0.01). From the October joining, TD ewes had a higher weaning rate than BD ewes which were higher than BLM ewes (P < 0.01), but ewe type was not significant for the other two joinings. Over the three joinings there were no differences between the ewe types in the number of lambings per year or percentage of lambs weaned, but BD had more lambs born (239¦ 7%) than TD (212¦5%) and BLM (181¦5%). Analyses of the components of reproduction that contributed to overall lamb production showed that although more than 95% of ewes expressed oestrus in each season, fertility and litter size were higher from the February joining, while lamb survival was lower following the June joining. Ewe crossbred type was significant (P < 0.01) for litter size in all seasons. Litter size for BD ewes was 1.9 to 2.0, and for TD ewes was 1.6 to 1.7 at all seasons, while that for BLM ewes was 1.7 from February and 1.2 and 1.4 from October and June joinings respectively. The effects of ewe liveweight at joining and liveweight gain over joining were variable over the three joinings, but were generally small. BD ewes carrying the F gene tended to have a higher percentage of lambs born and lower percentage of lambs weaned than non-carriers. There was also a decline in lamb production, especially fertility and lamb survival, with ewe age among BD and TD ewes. Implications for production systems in the lamb industry are discussed.