Feed efficiency and resilience in dairy ewes subjected to a nutritional challenge

It is currently uncertain how selection of more efficient animals might affect other traits such as resilience (which, in this context, is defined as the ability of an animal to sustain or revert quickly to its previous production level and health status after a disturbance), especially in small ruminants. However, improving, or at least maintaining, resilience is of utmost importance to ensure livestock production in the face of external perturbances, which are expected to become more prevalent in the near future due to climate change and global instability. This study was conducted to investigate whether a nutritional challenge consisting of animals receiving only 70% of their voluntary feed intake (DMI) for 26 d, might differentially affect the response of high and low feed efficiency (FE) in sheep. To meet this aim, residual feed intake (RFI), as a proxy of FE, was calculated in 40 lactating ewes fed a total mixed ration ad libitum. Using the RFI values, the ewes with the highest (H-FE; n = 8) and the lowest (L-FE; n = 8) FE were selected and subjected to the nutritional challenge. After the feed restriction, all sheep were again fed ad libitum for a further 25 d. Temporal patterns of variation in animal performance, ruminal fermentation, and blood and milk metabolites in response to, and recovery from, the underfeeding were examined in H-FE versus L-FE. More efficient ewes (H-FE) tended to eat less than less efficient ewes (L-FE) for the same level of production. Linear regressions for DMI and milk yield data showed that time-series response to the challenge was comparable in L-FE and H-FE. Despite temporal changes due to underfeeding, both FE divergent groups displayed a similar response to, and recovery from, the challenge with no significant differences in the temporal patterns of variation of the parameters analyzed, except for a tendency to higher plasma glucose in the L-FE ewes. These results challenge the general hypothesis that more efficient animals would be less resilient, but further research is still needed on the relationship and possible trade-offs between high efficiency and resilience.