Identification of Two Causal Mutations Associated with Milk Fat Content and Milk Fatty Acid Composition in Goats

In the framework of the "Phénofinlait" (www.phenofinlait.fr) and the "3SR" (www.3srbreeding.eu) projects, a large daughter design has been carried out in commercial farms for mapping traits in French dairy goats including milk production and fatty acid content estimated by mid-infrared spectra.

2,254 goats and their 20 artificial insemination sires were genotyped with the GoatSNP50 chip. After standard quality controls 49,647 SNPs were validated. QTL detection was performed using the QTLmap software.

Among the numerous QTL detected, a major QTL was found on CHI 14 associated with both the fat content and the fatty acid composition of milk in the region of the DGAT1 gene, which codes for a key enzyme involved in triglyceride synthesis in milk. DGAT1 sequencing in the 20 sires revealed two missense mutations, which were subsequently genotyped on a larger population of AI bucks. The first mutation was found only in the Saanen breed with a frequency of about 3%; the second mutation was present in both breeds with a frequency of 6% and 14% in Alpine and Saanen breeds, respectively. These two mutations seem to be associated with reduction of fat content (First mutation: -0.89g/kg in Saanen; second mutation: -1.19g/kg and -1.31g/kg in Saanen and Alpine respectively, for heterozygous animals), changes in fatty acid composition and increase in protein content. In order to validate the causality of the mutations, the different versions of the protein have been produced by a baculovirus system and first results obtained with CGFID show a reduced activity for mutant recombinant proteins.