Association between ovine Stearoyl-CoA desaturase gene polymorphism and the conjugated linoleic acid content in sheep milk fat: results of a positional candidate gene study

The aims of the study were the fine mapping of one QTL found for Conjugated Linoleic Acid (CLA) and Vaccenic Acid (VA) ratio on OAR 22 in a Sardinian x Lacaune backcross population and validating the QTL in the Sardinian pure breed. Fine-mapping was performed adding 7 microsatellites to the three previously used. The new QTL detection analysis highlighted the presence of one highly significant (p<0.00001) QTL with the most probable location at 35 cM corresponding to the position of the stearoyl coenzyme A desaturase (SCD) gene on the available maps. SCD represents a strong positional candidate gene since is a key enzyme responsible for ∆9-desaturation of fatty acids. The sire and twenty-eight ewes of the most significant family were selected to sequence the Scd gene: fourteen from the low and fourteen from the high tails of CLA and VA ratio. The sire resulted heterozygous C/T at intron 4 (3295 C>T on GenBank AH011188 Capra hircus SCD gene). Among the 14 animals of the high tail 13 inherited the T allele. Among the 14 animals of the low tail 13 inherited the C allele. The 3 other informative sires resulted homozygous C/C. The found QTL resulted segregating in three 7/8 families. All the 7/8 sires resulted homozygous C/C at the SNP found. Even if one significant polymorphism has been found, it does not allow the immediate application of MAS or GAS. However, the high significance of the QTL suggests that the undergoing studies will be successful to detect the causative mutations.