Breeding objectives for sheep derived from economic analysis of production systems show that litter size (LS) has a significant impact on profitability. Increasing LS can lead to increased income because more surplus animals are available for sale, but this comes at the expense of higher costs associated with increased feed requirements for ewes during pregnancy and lactation, and for finishing larger numbers of lambs. Poorer lamb survival in large litters also has an impact on costs. For these reasons the economic value for LS should be determined from a realistic bioeconomic model that accounts for the relationship between LS, feed cost and lamb survival, in addition to other economically important traits. This is particularly important when evaluating the importance of LS in harsh environments.
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