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

Abstract

Simulating a consequence of a climate change event on feed availability, responses of Mediterranean meat ewes facing an acute undernutritional 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 NEFA, β-OHB, glucose, urea, tri-iodothyronine (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 effects on lambs’ growth. The two-day 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 post-challenge levels. BW, BCS, DFT or DMI were also affected by parity (MULT>PRIM) but not by genetic line. Plasma NEFA, β-OHB, glucose, urea and T3 responded well to CHA with drops in T3, urea and glucose levels, whereas NEFA and β-OHB significantly increased after CHA. MULT ewes presented sharper β-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 in 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.