Romane sheep divergently selected on residual feed intake: consequences on production and feeding behaviour traits

Breeding companies are highly interested in including feed efficiency into their breeding programmes because of the economic and environmental benefits this would bring. We developed divergent lines on residual feed intake (RFI) in the Romane breed in order to estimate the consequences of RFI selection on other traits. In this experiment, RFI was phenotyped in growing lambs under an ad libitum low-energy concentrate diet, distributed through automated concentrate feeders, during 6-week test periods. The divergent selection experiment encompasses five generations of selection, and a total of 821 male lambs were phenotyped for production, feed efficiency and feeding behaviour traits. After five generations of selection, the difference between the efficient and less efficient lines reached 2.6 genetic SD, and efficient lambs ate on average 9.36% less concentrate than less efficient lambs. No significant differences in production traits were observed between both lines, except for on-farm breeding values, with daughters from efficient rams having higher estimated breeding values (EBVs) for prolificacy but lower EBVs for maternal traits. Significant differences between both lines were observed for feeding behaviour traits. The efficient lambs visited the feeders less and tend to spend less time in feeding activity. Less efficient lambs had a marked hourly feed intake pattern compared to efficient lambs. Nevertheless, the genetic correlations between RFI and production or behaviour traits were of low magnitude (from -0.33 to 0.24 with conformation score and BW at the beginning of the test, respectively), with most of the estimates being close to zero. This divergent experiment demonstrated that selecting RFI is feasible with low impacts on production traits, but particular caution must be paid to prolificacy and maternal traits to avoid any undesirable changes in these important traits. This also illustrated that feeding behaviour is different in efficient and less efficient animals, which provides clues to further investigate the mechanisms underlying feed efficiency in meat sheep.