Genetic×environment variation in sheep lines bred for divergent resistance to strongyle infection.

Guillaume Sallé,Céline Marquis,Philippe Jacquiet,Marie‐Madeleine Mialon,Gwenola Tosser‐Klopp,Delphine Serreau,Véronique Deiss,Jacques Cortet,Frédéric Bouvier,Didier Marcon,Christine Koch,Alexandra Blanchard,Carole Moreno‐Romieux

doi:10.1111/eva.13294

Abstract

Drug‐resistant parasites threaten livestock production. Breeding more resistant hosts could be a sustainable control strategy. Environmental variation linked to animal management practices or to parasite species turnover across farms may however alter the expression of genetic potential. We created sheep lines with high or low resistance to Haemonchus contortus and achieved significant divergence on both phenotypic and genetic scales. We exposed both lines to chronic stress or to the infection by another parasite Trichostrongylus colubriformis, to test for genotype‐by‐environment and genotype‐by‐parasite species interactions respectively. Between‐line divergence remained significant following chronic stress exposure although between‐family variation was found. Significant genotype‐by‐parasite interaction was found although H. contortus‐resistant lambs remained more resistant against T. colubriformis. Growth curves were not altered by the selection process although resistant lambs were lighter after the second round of divergence, before any infection took place. Breeding for resistance is a sustainable strategy but allowance needs to be made for environmental perturbations and worm species.

Highlights

Gastro-intestinal nematodes (GIN) impose a significant burden to human health and livestock worldwide
We considered pedigree-based breeding values as they were available across generations and were strongly correlated with Genomic estimated breeding values (geBVs). estimated breeding values (eBVs) were estimated from recorded phenotypes in G0, G1 and G2 individuals using a mixed model including fixed environmental effects and a random individual effect estimated from the pedigree relationship matrix as implemented in the AIReml software
Our work investigated how directional selection for contrasting levels of resistance to GIN infection would affect expression of sheep potential towards environmental change

Summary

| INTRODUCTION

Gastro-intestinal nematodes (GIN) impose a significant burden to human health and livestock worldwide. EBVs for first and second infection FEC were computed using a model including known fixed effects (litter size, sex) and an individual random effect estimated from the pedigree relationship matrix Their geBVs were subsequently estimated using their genotype information and TA B L E 1 Metadata associated with considered QTL for selection of G1 lambs. Responses to selection for FEC at first and second infection or across infections were evaluated within each generation and each line by regressing individual random effects from H. contortus-infected offspring upon their respective midparent values, computed as the average value of each lamb's sire and dam (Falconer & Mackay, 1996) This regression coefficient provides an estimate for realized heritability (Falconer & Mackay, 1996) and was used to establish the asymmetry of response between resistant and susceptible lines. Pearson's correlations were estimated with the rcorr() function from the Hmisc package (Harrell & Dupont, 2017)

| RESULTS

Findings

| DISCUSSION