Variation in the stearoyl-CoA desaturase gene (<i>SCD</i>) and its influence on milk fatty acid composition in late-lactation dairy cattle grazed on pasture

Abstract

Abstract. Gene markers have become useful tools for improving animal genetics and breeding since they improve the accuracy of selection for superior breeding stock. In this study, the stearoyl-CoA desaturase (Δ-9-desaturase) gene (SCD) was investigated in New Zealand pasture-grazed Holstein–Friesian × Jersey cows. Three nucleotide substitutions were identified in exon 5 of the gene (c.702A/G, c.762T/C and c.878C/T), and a single nucleotide substitution was identified in intron 5 (c.880+105A/G). The c.878C/T substitution would, if expressed, result in the amino acid substitution p.A293V. Four nucleotide substitutions (c.*1783A/G, c.*1883C/T, c.*1984G/A and c.*2066T/C/G) were identified in the 3′-untranslated region (3′-UTR), and these resulted in three nucleotide sequence variants (named a, b and c). The sequence that would encode valine (V) at position 293 of SCD was linked to 3′-UTR variant a, and the sequence that would encode alanine (A) was linked to variants b and c. The frequency of the genotypes was as follows: VV (equivalent to aa: 15.1 %), VA (equivalent to ab+ac: 50.0 %) and AA (equivalent to bb+cc+bc: 34.9 %). The cows with the V variant produced less C10:1, C12:1 and C14:1 fatty acid (FA) but more C10:0, C11:0, C14:0, C16:1 and C18:2 FA than the A variant cows (P<0.001). Effects of c.*1783A/G and c.*2066T/C/G on milk fat composition were also found for the AA cows. The presence of c was associated with decreased levels of C16:1 (P<0.001), C17:1 (P=0.001), C18:2 cis-9, trans-13 (P=0.045), C18:2 cis-9, trans-12 (P=0.018) FA and C16:1 FA index (P<0.001). The presence of b was associated with increased levels of C13:0 iso FAs (P<0.001), monounsaturated FA (MUFA; P=0.002) and C12:1 (P<0.001).