Body weight and body condition score variations in Romane ewes: Intraflock variability in their dynamics and magnitude over multiple production cycles

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Breeding for resilience requires a better understanding of intra-flock variability and the related mechanisms responsible for robustness traits. Among such traits, the animals’ ability to cope with feed fluctuations by mobilizing or restoring body reserves (BR) is a key mechanism in ruminants. The objective of this work was to characterize individual variability in BR dynamics in productive Romane ewes reared in extensive conditions. The BR dynamics profiles were characterized by combining individual longitudinal measurements of BW and BCS over several production cycles. Historical data, including up to 2,628 records per trait distributed in 1,146 ewes, underwent cluster analysis. Two to 4 trajectories were observed for BW depending on the cycle, while 3 trajectories were always found for BCS, whatever the cycle. Most trajectories suggested that BR dynamics were similar but that the level of BR differed between ewes. Nevertheless, some trajectories suggested that both BR dynamics and levels were different for a proportion of ewes. The distribution of the ewes between the trajectories was explained by the ewe’s age, litter size, and individual variability. Many individual trajectories remained the same throughout a ewe’s life, whatever the age, parity, or litter size. Our results demonstrate the relevance of using BW and BCS for characterizing the diversity of BR mobilization-accretion profiles in sheep in a long timespan perspective. This is probably the first report of proven intra-flock variability in the adaptive capacities of grazing sheep. Nevertheless, further research efforts are needed to complete the characterization of BR dynamics by including other physiological (e.g., a set of plasma metabolites and hormones) and zootechnical parameters to obtain new insights into the complex mechanisms determining individual robustness.