Intra-flock variability in the body reserve dynamics of meat sheep by analyzing BW and body condition score variations over multiple production cycles

Abstract

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 body condition scores (BCS) over several production cycles. Historical data, including up to 2628 records per trait distributed in 1146 ewes, underwent cluster analysis. Two to four trajectories were observed for BW depending on the cycle, while three trajectories were found for BCS, whatever the cycle. Most trajectories suggested that BR dynamics were similar but the level of BR may differ between ewes. Nevertheless, some trajectories suggested that both BR dynamics and levels were different for a proportion of ewes. Clustering on BW and BCS profiles adjusted for individual level trends, resulted in differences only in the level of BW or BCS, rather than differences in trajectories. Thus, the overall shape of trajectories was not changed considering or not the individual level trend across cycles. In addition to individual variability, the ewe’s age at first lambing and litter size contributed to the distribution of the ewes between the trajectories. Regarding the entire productive life, three trajectories were observed for BW and BCS changes over three productive cycles. Increase in BW at each cycle suggested that ewes kept growing up until 3 to 4 years old in our conditions. Similar alternation of BCS gains and losses across cycles suggested BR dynamics might be repeatable. Many individual trajectories remained the same throughout a ewe’s life, whatever the age at first lambing, parity or litter size. Our results demonstrate the relevance of using BW and BCS changes for characterizing the diversity of BR mobilization–accretion profiles in sheep in a long timespan perspective.

Relationships between body reserve dynamics and rearing performances in meat ewes1

“…The relationships between the BW and BCS profiles (i.e., the identified clusters reported by Macé et al, 2019) and the ewes' rearing performances at the intraparity level are provided in Tables 2 and 3. At PAR 1, all of the parameters were affected by the BW profile with the exception of litterADG3m and litterSurv.…”

“…Several BW and BCS profiles were obtained (see figures 1 and 2 in Macé et al, 2019). This work has previously been published, and details about the procedures used are available in Macé et al (2019). In the present study, the relationships between the previously obtained BW and BCS profiles and PERF traits were analyzed and interpreted.…”

“…The same two operators systematically recorded the BCS measurements over the 14-yr period and underwent regular training sessions for calibration and adjustments while using the scale described by Russel et al (1969), which was subdivided into 0.1 increments ranging from 1 (emaciated) to 5 (obese). To characterize BR changes over time (i.e., accretion or mobilization phases), differences in BW or BCS between pairs of physiological stages were established, calculated, and used for interpretation as described by Macé et al (2018Macé et al ( , 2019. The differences in BW and BCS between different stages were calculated and analyzed (i.e.,…”

“…Cluster analyses have been performed previously to investigate the variability of individual BW and BCS profiles during each production cycle of the ewe with no assumptions regarding the factors of variation. Several BW and BCS profiles were obtained (see figures 1 and 2 in Macé et al, 2019). This work has previously been published, and details about the procedures used are available in Macé et al (2019).…”

“…We previously provided evidence of the existence of different BR profiles with a genetically driven component in a Romane meat sheep population in France (Macé et al, 2018(Macé et al, , 2019. The first objective of this work was to compare PERF traits between ewes with different BR profiles over several production cycles.…”