Season and reproductive status rather than genetics factors influence change in ewe weight and fat over time. 1. Analysis of crossbred ewes

García

Kövér

et al. 2020

Preprint

In situations of negative energy balance (NEB) due to feed scarcity or high physiological demands, body energy reserves (BR), mainly stored in adipose tissues, become the main sources of energy for ruminants. The capacity to mobilize and restore such BRs in response to different challenges is of major concern in the current context of breeding for resilience. Body condition score (BCS) is a common, practical indicator of BR variations throughout successive productive cycles, and quantitative tools for characterizing such dynamics at the individual level are still lacking. The main objective of this work was to characterize body condition dynamics in terms of BR mobilization and accretion capacities of meat sheep during their productive lifespan through a modelling approach. The animal model used in this work was the reproductive meat ewe (n = 1478) reared in extensive rangeland. Regular measurements of BCS for each productive cycle were used as the indicator of BR variations. A hybrid mathematical model and a web interface, called PhenoBR, was developed to characterize ewes' BCS variations through four synthetic and biologically meaningful parameters for each productive cycle i: BR accretion rate, BR mobilization rate, plus the time of onset and the duration of the BR mobilization. The model converged for all the ewes included in the analysis. Estimation of the parameters indicated the inter-individual variability for BR accretion and mobilization rates, and for the length of the mobilization period. Body reserve mobilization rates were closely correlated between productive cycles. Significant correlations between BR mobilization and accretion rates suggest that the two processes are biologically linked. Parameters kp and kb decreased as parity increased. BR mobilization rate and duration increased as litter size increased, while BR accretion rate decreased. Individual characterization of animals by these parameters makes it possible to rank them for their efficiency in the use of body reserves when facing NEB challenges. Such parameters could contribute to better management and decision-making by farmers and advisors, e.g. by adapting feeding systems to the individual characteristics of BR dynamics, or by geneticists as criteria to develop future animal breeding programs including BR dynamics for more robust and resilient animals.

Section: Discussionsupporting

confidence: 71%

PhenoBR: a model to phenotype body condition dynamics in meat sheep

García

Kövér

et al. 2020

Preprint

“…This is particularly true for ruminants, for which future farming systems are expected to rely mostly on grasslands and rangelands. It is well known that some typical physiological and environmentally driven factors have an effect on BR dynamics as reported by the analysis of the relationships between various ewe-rearing performances (PERF) or mothering abilities and their body condition (Walkom et al, 2014a(Walkom et al, , 2014bWalkom and Brown, 2017). Walkom and Brown (2017) reported very strong correlations between measurements across the production cycle for BW and BCS along with weak genetic relationships of BW and BCS change traits.…”

Section: Introductionmentioning

confidence: 99%

Relationships between body reserve dynamics and rearing performances in meat ewes1

Journal of Animal Science

Hazard

Carriere³

et al. 2019

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.

“…Considering the existing genetic variability for energetic body reserve traits previously reported in sheep (BANOS et al 2005;WALKOM et al 2014a;MACÉ et al 2018), the aim of the present study was to provide the first characterization of the genetic architecture that controls body condition in productive ewes. This was achieved by a genome-wide association study (GWAS) of a set of body reserve (BR) traits measured at key physiological stages of the productive cycle in Romane ewes.…”

Section: Discussionmentioning

confidence: 99%

“…2014), depending on the breed and the physiological stage of the measurement (K oenen et al . 2001; W alkom et al . 2014a; M acé et al .…”

Section: Introductionmentioning

confidence: 99%

Genome-wide analyses reveal a strong association between LEPR gene variants and body fat reserves in ewes

Gonzalez-Garcia

Foulquie

et al. 2021

Preprint

Among the adaptive capacities of animals, the management of energetic body reserves (BR) through the BR mobilization and accretion processes (BR dynamics, BRD) has become an increasingly valuable attribute for livestock sustainability, allowing animals to cope with more variable environments. BRD has previously been reported to be heritable in ruminants. In the present study, we conducted genome-wide studies (GWAS) in sheep to determine genetic variants associated with BRD. BR levels and BR changes over time were obtained through body condition score measurements at eight physiological stages throughout each productive cycle in Romane ewes (n=1034) and were used as phenotypes for GWAS. After quality controls and imputation, 48,513 single nucleotide polymorphisms (SNP) were included in the GWAS. Among the QTLs identified, a major QTL associated with BR levels during pregnancy and lactation was identified on chromosome 1. In this region, several significant SNPs mapped to the leptin receptor gene (LEPR), among which one SNP mapped to the coding sequence. The point mutation induces the p.P1019S substitution in the cytoplasmic domain, close to tyrosine phosphorylation sites. The frequency of the SNP associated with increased BR levels was 32%, and the LEPR genotype explained up to 5% of the variance of the trait. These results provide strong evidence for involvement of LEPR in the regulation of BRD in sheep and highlight it as a major candidate for improving adaptive capacities.