Reproductive performance of progesterone synchronised IGF‐1 selection line ewes

It has been suggested that selection based on insulin‐like growth factor‐1 (IGF‐1) concentrations could be used as a mechanism to improve efficiency of growth in young animals. However, there is the strong possibility that selection on IGF‐1 levels could cause correlated changes in other traits. The present study was designed to determine if selection based on phenotypic IGF‐1 concentrations has any impact on reproductive performance of ewes. In study one, the breeding performance and ovulation rate of oestrus‐synchronised ewes selected for either “Low” or “High” phenotypic IGF‐1 concentrations, and that of a control line, were compared. In study two, ewes were also superovulated using eCG and the above parameters measured. In study one, both Low and High line ewes were less (P < 0.05) likely to be bred in the 4‐day period post‐synchronisation only, and more (P < 0.05) likely to return to service than Control ewes. These relationships were not observed in study two. In study two, but not in study...