Short-term responses of meat ewes facing an acute nutritional challenge in early-mid lactation

Simulating a consequence of a climate change event on feed availability, responses of Mediterranean meat ewes facing an acute under nutritional challenge (CHA; i.e., fed only low nutritional value cereal straw) were evaluated at a sensitive physiological stage (i.e., early suckling). Forty Romane ewes were chosen at early-mid pregnancy (around 2 mo) according to parity (20 primiparous, PRIM; 20 multiparous, MULT); feed efficiency genetic line of their sires (residual feed intake [RFI]; efficient, RFI-, n = 10 per parity; inefficient, RFI+, n = 10 per parity); litter size (i.e., bearing twins, diagnosed by ultrasonography); body weight (BW, kg) and body condition score (BCS) (initial BW and BCS [mean +/- SD]: 51.6 +/- 7.41 kg; 2.5 +/- 0.20, respectively; representing flock' averages per parity). Effects on dry matter intake (DMI), ewes' BW and BCS, subcutaneous dorsal fat thickness (DFT), energy metabolism (plasma non-esterified fatty acids [NEFA], beta-hydroxybutyrate (beta-OHB), glucose, urea, triiodothyronine [T3]), and lambs' growth (BW and average daily gain [ADG]; g/d) were examined before, during and after CHA. Individuals' profiles of the response-recovery to CHA were described using a piecewise mixed-effects model. The fixed effect of parity and genetic line and the random effect of individual (ewe) were considered. A linear mixed-effects model was fitted to explore the effects on lambs' growth. The 2-d straw-only CHA had significant effects on most of the recorded parameters. Meaningful drops and recoveries were observed on ewes' DMI, BW, and DFT with effect on postchallenge levels. BW, BCS, DFT, or DMI were also affected by parity (MULT > PRIM) but not by genetic line. Plasma NEFA, beta-OHB, glucose, urea, and T3 responded well to CHA with drops in T3, urea, and glucose levels, whereas NEFA and beta-OHB significantly increased after CHA. MULT ewes presented sharper beta-OHB recovery from CHA than PRIM (P <= 0.05). With this study, we provide tangible and necessary data for an emerging field of research. Our results give new insights into how such a short and abrupt CHA affects some key zootechnical and physiological parameters, and to what extent the impacts of CHA and the ewes' response-recovery are influenced. It also revealed potential between-individual differences in the adaptive capacities of ewes, which require further exploration. Climate change is imposing unexpected nutritional challenges to livestock (in time and magnitude). In this context, the individual adaptive capacity to respond to, and recover from those environmental fluctuations is an increasingly important trait to be considered in the daily management operations by the farmer and in future selection programs. The objective of this work was to characterize the responses of meat ewes when facing an abrupt nutritional challenges (i.e., the only feed available being a cereal straw with a very low nutritional value) at a very sensitive physiological stage (i.e., after lambing). Results provide new insights into how a strong nutritional challenges affects some key zootechnical and physiological parameters. The level of synchronization and/or interdependency of biological mechanisms responsible for two different but somehow inter-related traits (i.e., feed efficiency and individual robustness or resilience) is an original aspect addressed in the current study. It helps to understand to what extent the impacts of the challenge and the ewes' potential recovery are influenced by the individual nature of the animals (i.e., inter-individual differences in the responses).