Relationships between body reserves dynamics and ewes rearing performances in meat sheep

Since a few years, breeders are looking to select more robust animals in order to improve adaptation to more challenging environments. One expression of such robustness is a suitable cyclic alternation of accretion and mobilization of body reserves (BR) i.e. BR dynamics. In a previous study, we characterized several BR trajectories based on body condition score (BCS) and body weight (BW) measurements regularly recorded according to a physiological stages schedule. In addition, in a previous multi-traits approach of BR changes over time we found that BR accretion and mobilization were heritable traits and genetically linked. The objectives of the present study were therefore: (1) to evaluate the link between BR trajectories and ewes rearing performances and; (2) to estimate the genetic correlations between BR changes and ewes rearing performances. By using records from 1,146 productive Romane ewes, their rearing performances were estimated by analysing key parameters like the total weight of the litter at lambing and at weaning, and the average daily gain (ADG) of the lamb during their first, second and third month of life. The effects of the BR trajectories of the dam were also tested. Genetic correlations were estimated between the ewes’ BR changes through time and their rearing performances, by conducting animal mixed model analyses. Overall, ewes presenting a stronger decrease in their trajectories during the BR mobilization period, showed superior rearing performances. Negative favourable correlations were found between BR mobilization and the total litter weight at lambing (-0.42±0.15) and between BR mobilization and ADG of lambs during the first and second month of suckling (-0.29±0.14). Positive favourable correlations were found between BR accretion and litter weight at birth (0.42±0.15) and between BR accretion and the lamb ADG during the first month of life (0.37±0.15). Present results suggest that BR dynamics could be considered in genetic selection programs to improve animals’ resilience while enhancing ewes’ performances when facing external challenges.