Genetic and genomic studies in ovine mastitis

Mastitis is a strong financial and animal welfare concern in both dairy and meat-producing sheep. In this review article, we summarized recent advances in research on genomic of mastitis resistance in sheep. Heritability estimates for mastitis-related traits such as somatic cell scores or milk bacteriological counting have confirmed a genetic basis for mastitis resistance. Recent outputs from genomic-based studies comprising genome-wide associations, the identification of one causal mutation as well as gene expression studies have highlighted regions of the genome, and possible genes and mechanisms underlying the resistance trait. Part of genomic regions was common among breeds and populations, and have testified to the partial sharing of mastitis-related genetic mechanisms between different distant dairy sheep populations. Accumulating genetic data, however, have underlined the polygenic nature of the trait and the complexity of the resistance phenotype. Both quantitative and genomic analyses have further revealed trade-offs and synergies under genetic control between mastitis resistance and other efficiency (milk production) and resilience related traits (udder type traits and metabolic disease). We have also reported how phenotypic, pedigree and genomic information has been used in sheep breeding, the aim being to improve the animals’ health and welfare, the hygienic quality of milk products and overall efficiency and resilience.