Relationships between body reserve dynamics and rearing performances in meat ewes1

Abstract

The main objective of this work was to study the relationships between body reserve (BR) dynamics and rearing performance (PERF) traits in ewes from a Romane meat sheep flock managed extensively on “Causse” rangelands in the south of France. Flock records were used to generate data sets covering 14 lambing years (YR). The data set included 1,146 ewes with 2 ages of first lambing (AGE), 3 parities (PAR), and 4 litter sizes (LS). Repeated measurements of the BW and BCS were used as indicators of BR. The ewe PERF traits recorded were indirect measurements for maternal abilities and included prolificacy, litter weight and lamb BW at lambing and weaning, ADG at 1, 2, and 3 mo after lambing, and litter survival from lambing to weaning. The effects of different BW and BCS trajectories (e.g., changes in BW and BCS across the production cycle), previously been characterized in the same animals, on PERF traits were investigated. Such trajectories reflected different profiles at the intraflock level in the dynamics of BR mobilization–accretion cycles. Genetic relationships between BR and PERF traits were assessed. All the fixed variables considered (i.e., YR, AGE, PAR, LS, and SEX ratio of the litter) have significant effects on the PERF traits. Similarly, BW trajectories had an effect on the PERF traits across the 3 PARs studied, particularly during the first cycle (PAR 1). The BCS trajectories only affected prolificacy, lamb BW at birth, and litter survival. Most of the PERF traits considered here showed moderate heritabilities (0.17–0.23) except for prolificacy, the lamb growth rate during the third month and litter survival which showed very low heritabilities. With exception of litter survival and prolificacy, ewe PERF traits were genetically, strongly, and positively correlated with BW whatever the physiological stage. A few weak genetic correlations were found between BCS and PERF traits. As illustrated by BW and BCS changes over time, favorable genetic correlations were found, even if few and moderate, between BR accretion or mobilization and PERF traits, particularly for prolificacy and litter weight at birth. In conclusion, our results show significant relationships between BR dynamics and PERF traits in ewes, which could be considered in future sheep selection programs aiming to improve robustness.

Impact of Body Reserves Dynamic on Productivity and Reproductive Performance in Fat-Tail and Thin-Tail Sheep Breeds over Contrasting Production Cycles

“…The BR mobilization continued intensively for all breeds and for both years during the lambing and suckling stages, due to the highest energy needs induced by these physiological stages and accompanied by food scarcity. The BW and BCS profiles recorded in the current study in such conditions are consistent with the previously described dynamics between mating and weaning [ 1 , 5 , 16 ], showing the use of BR from mid-pregnancy until the end of the suckling period, which is revealed by a decrease in the BCS [ 5 ]. During lactation, irrespective of breed and lambing BCS, all ewes mobilize their BR to produce milk, even for ewes with poor BCS.…”

“…The BW and BCS were simultaneously assessed with the aim of an effective description of the dynamics of body reserves in ewes, covering both mobilization and accretion processes [ 2 , 24 ]. Regardless of the breed, the BW of all ewes increased during pregnancy in relationship to the anabolism of pregnancy combined with the fetus growth and development [ 5 , 25 ]. However, the BCS at both the lumbar and caudal levels recorded a decrease during this stage; this decrease reflects the decrease in the corporal mass of ewes and confirms the better accuracy of the BCS as a tool to assess BR.…”

“…The correlations of both daily gains with the BCS variation were not significant ( Table 5 ). By contrast, strong positive genetic correlations between ewes’ BR (BW or BCS) and lambs’ growth parameters were reported [ 4 , 5 , 35 ].…”

“…However, they face the challenges of frequent climatic perturbation associated with climate change, continuous rising costs, and seasonal feed restrictions [ 1 , 2 , 3 ]. In such situations, sheep production needs to improve its ability to adapt to the changing production conditions, primarily by breeding robust and resilient animals [ 4 , 5 , 6 ]. Hence, in the future, breeding strategies will include robust animals able to adapt to variations in feed availability [ 7 , 8 ].…”

Short-, Medium- and Long-Term Metabolic Responses of Adult Meat Ewes Subjected to Nutritional and β-Adrenergic Challenges

“…In highly productive ruminants, there is evidence that their reliance on body energy reserves (BR) is increased, and body mass is reduced to fit significant energy requirements [ 2 ]. The efficiency of BR mobilization-accretion processes, to overcome undernutrition, is therefore recognized as an essential mechanism in ruminants [ 3 , 4 , 5 , 6 ]. These processes contribute to maintaining the resilience of the flock under a fluctuating feed supply, such as in tropical [ 7 ] or Mediterranean regions, where seasonal forage availability is highly fluctuating.…”