Genetic evaluation of crossbred lamb production. 5. Age of puberty and lambing performance of yearling crossbred ewes
The age and liveweight at puberty were evaluated in 2155 crossbred ewe lambs at 2 sites over 3 years. A separate dataset examined the lambing performance of 1177 crossbred ewe lambs that were joined naturally at ~7 months of age at 2 sites over 3 years and also their lambing performances in the subsequent 2 years. The ewe lambs were the progeny of Merino dams and sires from several breeds including Border Leicester, East Friesian, Finnsheep, Coopworth, White Suffolk, Corriedale, and Booroola Leicester. Overall, 85% of the ewe lambs reached puberty (detected by teasers) in their first autumn at an average age of 248 days and liveweight of 42 kg. There was significant variation in age and weight at puberty (P < 0.01) among the site and year cohorts of ewes. Sire breed was significant for weight (P < 0.01) but not age at puberty. Of the crossbred ewe lambs joined at 7 months of age, 54% lambed with an average litter size of 1.31 and 49% of lambs were weaned from the ewes joined. There was a significant site effect for all reproduction traits (P < 0.01), with the higher performance at one site associated with higher liveweight at joining. Maternal sire breed was significant for all reproduction traits (P < 0.01) and there was considerable variation between sires within sire breeds. Ewes that reared lambs in their first year weaned 12% more lambs per year in their second and third years compared with ewes that failed to lamb or rear any lambs at 1 year of age. The results demonstrate that lamb weaning rates of 90% or more can be achieved from crossbred ewe lambs with optimal genetics and management. The opportunities for improving productivity by joining crossbred ewe lambs and the selection and management considerations required for successful joinings and lambings are reviewed and discussed.