Improving the reproductive performance of ewe lambs – Management guidelines, economic analysis and decision support tools

Summary

​Increasing the number of ewes joined to lamb as yearlings at 12 to 15 months could be an effective avenue to rapidly build ewe numbers and increase lamb supply. However, the reproductive performance of ewe lambs is much lower and more variable than that achieved by adult ewes. A lack of information on the longer-term impacts of joining ewe lambs, both on the young ewe and her offspring, plus the cost-effectiveness of joining ewe lambs has also contributed to relatively poor adoption of the practice. Previous projects (B.LSM.0038 and B.PDS.0903) identified the importance of using teasers, liveweight at joining, growth rate during joining and sire genetics to improve the reproductive rate of ewe lambs. The current project extended this earlier work and completed a metanalysis of datasets relating to the reproductive performance of ewe lambs from Australia and New Zealand, including the effects of: (i) liveweight profile of ewe lambs on the birth weight, survival and growth of their progeny to weaning; (ii) carryover effects of ewe lamb reproductive performance on their hogget reproductive performance, and (iii) growth, wool production and reproductive performance of progeny born to ewe lambs compared to progeny born to adult ewes. The project also used the outputs from this metanalysis to inform economic modelling using MIDAS to developed management guidelines to cost-effectively improve the reproductive performance from ewe lambs. However, the number of scenarios modelled was limited and the determination of the management guidelines with respect to live weights profiles from weaning to joining, during joining, during pregnancy and between weaning and the 2 year old mating to maximise profitability were not clear. It also became apparent during this project that the prediction equations for energy requirement or intake capacity of maternal sheep require updating and hence the maternal component of this analysis could be incorrect. Additional analysis, using refined feeding standards for maternal ewes, across environments and different lambing times, plus lambing young ewes 1-2 months later that the adult flock, is still needed to formulate more robust management guidelines that optimise the profitability from joining ewe lambs.