Pleiotropic effect of the R96C mutation in the dairy sheep SOCS2 gene ; Effet pléiotrope de la mutation R96C dans le gène SOCS2 chez la brebis laitière

In this PhD thesis, we investigated a mutation in the SOCS2gene (Suppressor Of Cytokine Signaling 2) with a pleiotropic effect, i.e.it affects several traits of interest in the Lacaune dairy sheep. This mutation is unfavorable for mastitis resistance (udderinflammation), and favorable for growth and milk production traits.This point mutation (SNP -Single Nucleotide Polymorphism), located in the highly conserved binding domain of the SOCS-2 protein,causes the loss of functionality of the protein that is involved in a major signaling pathway in mammals:the JAK(Janus Kinase) / STAT (Signal Transducer and Activator of Transcription) pathway, regulating a large spectrum of cytokines and growth factors.The first objective of this PhD thesis was to provide a basis for considering this mutation in the context of genomic selection in the Lacaune breed. Weighted evaluation methods, and the addition of the SOCS2SNP among the chip markers, brought gains in accuracy on predictions (+3.99% and +0.26% respectively on average), suggesting the possibility of more efficient selection. The Gene Contentmethod was also interesting because it alloweddissociatingthe genetic value due to the SOCS2gene from that of the other genes (polygene). Thus, we have shown that the current selection in Lacaune breed allows reducing the frequency of the unfavorable SOCS2allele while improving the resistance to mastitis explained by the remaining part of the genome.The second objective was to study the effects of SOCS2on traits of interest not yet investigated: udder infection status and reproduction in females, and growth in males. Association studies with a 960 SNP chip, including SOCS2SNP, confirmed the effect of SOCS2on milk production and mammary inflammation, and showed a direct effect on infection using new fine phenotypes (bacteriology, clinical examinations). Linear models showed that the SOCS2mutation was associated withan increase in weight in young males (+1.5%), as observed in ewes, and a decrease in the artificial insemination success ...