Single nucleotide polymorphisms in the open reading frame of the stearoyl-CoA desaturase gene and resulting genetic variants in Canadian Holstein and Jersey cows.

Stearoyl-CoA desaturase (SCD) catalyzes the synthesis of conjugated linoleic acid (CLA) and mono-unsaturated fatty acids (MUFA) from their saturated counterparts in the mammary gland and adipose tissue of ruminant animals. We hypothesize that single nucleotide polymorphisms (SNPs) in the SCD gene account for some of the differences in SCD activity, and consequently for some of the variations in CLA and MUFA content of milk fat between Holsteins and Jersey cows and within these two breeds. We analyzed the open reading frame of the SCD gene of 44 Holsteins and 48 Jerseys for SNPs by sequencing. Three SNPs: 702A --> G, 762T --> C and 878C --> T were identified in both breeds and a further SNP, 435G --> A, was unique to Holsteins. The SNPs characterized four different genetic variants in Holsteins: A (G(435)A(702)T(762)C(878)), A1 (A(435)A(702)T(762)C(878)), B (G(435)G(702)C(762)T(878)) and B1 (A(435)G(702)C(762)T(878)), with only variants A and B in Jerseys. SNP 878C --> T resulted in a non-synonymous codon change while the rest resulted in synonymous codon changes giving rise to two protein variants, A having alanine and B having valine. Allele A was the most prevalent in the two breeds. These differences may, therefore, contribute to existing variations in CLA and fat content between and within Canadian Holstein and Jersey cows.