More Lambs per ewe lifetime through better genetic evaluation systems

Summary

​Data for progesterone concentration (a proxy measure for puberty), pre-joining weight and condition, and reproductive outcomes for pedigreed ewes joined to lamb as yearlings were obtained from 9 breeders in three states (NSW, VIC and SA) from 12 industry flocks, containing maternal, terminal and Merino breed types. The focus ewes (N=3296) were born in 2012, and were joined to first lamb as 1 year olds in 2013. Fertility levels ranged from 0% to 75% across flocks. Progesterone and fertility data combined suggest that the main factor contributing to variable yearling reproductive performance was failure to attain puberty. Progesterone concentrations were moderately heritable but not strongly correlated genetically or phenotypically with pre-joining weight or condition score. Therefore, progesterone levels were largely independent of genes controlling pre-joining weight and condition score. Low to moderate genetic correlations between pre-joining weight, condition score or progesterone and the number of lambs born (NLB) indicates that breeders cannot rely solely on these traits to provide indirect information on genetic merit for NLB in yearling ewes and that the reproductive performance itself needs to be recorded. However, estimates of genetic correlations suggest the accuracy of selection for NLB may be improved by data from these correlated traits.  More accurate estimates of genetic parameters are required to evaluate the expected changes in response to selection under alternative recording strategies involving correlated traits. Phenotypically, progesterone concentration was most strongly associated with fertility, whereas pre-joining weight and condition score were most strongly associated with litter size.