Interaction between stearoyl-coenzyme A desaturase polymorphism and feeding system in affecting the fatty acid profile of sheep cheese

Abstract

Stearoyl-coenzyme A desaturase (SCD) catalyses the synthesis of monounsaturated fatty acids, by introducing a cis double bond at the delta 9–10 position. The study investigated the effects of a polymorphism at the ovine SCD gene and its interaction with the inclusion of fresh forage in the diet on cheese fatty acid (FA) composition in Valle del Belice ewes. A region of 527 bp of the ovine SCD gene including the partial sequence of the promoter, the complete sequence of the 5’ UTR and exon 1 and the partial sequence of intron 1 were analyzed in order to identify the g.87C > A SNP located in the promoter region. A feeding trial was carried out using 16 Valle del Belice ewes selected on the basis of their genotype (6 CC and 10 AC). Each genetic group was fed, according to a latin square experimental design, with diets based on conserved or fresh forage, consisted of sulla hay (SH) or sulla green forage (SGF), integrated with 1 kg/d of concentrate feed. Cheese made from individual milk was analyzed for FA composition. The SCD genotype had no effect on cheese monounsaturated and polyunsaturated FA, whereas significantly influenced the desaturation activity, as demonstrated by the higher desaturation indices in the CC ewes compared to AC ewes (C14 index: 0.021 vs. 0.017; C18 index: 0.71 vs. 0.68; trans-vaccenic index: 0.38 vs. 0.32; p < .05). This result seems consistent with the possible role of this polymorphism on the enzyme desaturase synthesis and its activity in the mammary gland. However, this does not appear to be supported by the levels of monounsaturated FA or conjugated linoleic acid (CLA, C18:2c9t11) which were not affected by the g.87C > A polymorphism. The SGF diet significantly increased trans vaccenic, linoleic and CLA acids of cheese, compared to the SH diet (respectively: 2.30 vs. 1.31; 2.53 vs. 2.25; 1.00 vs. 0.80; p < .05). No significant interaction resulted, thus the effect of SCD genotype on desaturation indices was evident regardless of the diet. The results obtained, while showing an effect of SCD polymorphism on the level of desaturation, do not allow to highlight a role of the more favourable CC genotype in further improving the acidic composition of the cheese in health terms due to the presence of green forage in the diet. However, the genetic polymorphism of sheep SCD and its interaction with diet should be further investigated, given the lack of information on this species.