Residual feed efficiency established in a post-weaning growth test may not result in more efficient ewes on the range

Reduction of feed required for normal lamb and wool production could improve the profitability of sheep producers. Our objectives were to determine growth and feed efficiency traits of Targhee sheep receiving a growing diet as ewe-lambs (Exp. 1) and a maintenance diet as yearlings (Exp. 2). Furthermore, we compared the repeatability of these traits between the two experiments. Within each experiment, residual feed intake (RFI) was strongly correlated (0.77 and 0.89) with DMI and no relationships were detected between RFI and ADG or metabolic BW. The low-RFI group had a 19 and 29% reduction in DMI compared to the high-RFI group for Exp. 1 and 2, respectively. No differences were detected for wool fiber diameter change (Exp. 1) or hay digestibility (Exp. 2) among RFI groups (P ≥ 0.70). No significant correlations were detected for growth or feed efficiency traits between Exp. 1 and 2. These results suggest that considerable feed efficiency differences exist in ewe-lambs during active growth and yearlings at maintenance. However, based upon the lack of relationship between Exp. 1 and 2 for feed efficiency, the authors suggest that RFI established on a postweaning growth test may not result in more efficient ewes on the range.