Dietary linseed oil with or without malate increases conjugated linoleic acid and oleic acid in milk fat and lipoprotein lipase and stearoyl-coenzyme A desaturase gene expression in mammary gland and milk somatic cells of lactating goats

Supplementary dietary plant oils have the potential to alter milk fatty acid composition in ruminants as a result of changes in the amount and kind of fatty acid precursors. We hypothesized that linseed oil in combination with malate (a key propionate precursor in the rumen) would increase unsaturated fatty acids and specific gene expression in somatic cells and mammary glands of lactating goats. Twelve lactating goats were used in a 3 x 3 Latin square design. Treatments included the basal diet (CON), the CON plus 4% linseed oil (LO), and the CON plus 4% linseed oil and 2% dl-malate (LOM). Relative to CON, the LO and LOM supplements increased the daily intake of palmitic (16:0), stearic (18:0), oleic (18:1n-9), linoleic (18:2n-6), α-linolenic (18:3n-3), and y-linolenic acids (18:2n-6); α-linolenic acid intake was increased over 9-fold, from 6.77 to over 51 g/d (P < 0.02). The LO and LOM supplements increased daily milk yield, milk fat yield, and milk fat percentage (P < 0.05). The LOM supplement also increased milk lactose percentage and daily yield (P = 0.03). Both the LO and LOM supplements increased plasma glucose and total cholesterol and decreased plasma β-hydroxbutyrate concentrations (P = 0.03). The LO and LOM supplements increased concentrations of stearic acid; trans-vaccenic acid (TVA; 18:1trans-11); cis-9, trans-11 CLA; trans-10 cis-12 CLA; and α-linolenic acid in rumen fluid and increased the concentrations of oleic acid; TVA; cis-9, trans-11 CLA; trans-10, cis-12 CLA; and α-linolenic acid in plasma lipids and milk fat (P < 0.05). Conversely, the LO and LOM supplements decreased short- and medium-chain SFA, including lauric (12:0), myristic (14:0), and palmitic acids, in plasma and milk fat (P < 0.05). Relative mRNA levels for lipoprotein lipase and stearoyl-CoA desaturase (SCD) gene expression were increased in somatic cells and mammary gland tissue by LO and LOM (P < 0.05). We conclude that the higher intake and ruminal production of stearic acid promoted SCD gene expression in somatic cells and mammary tissue. Furthermore, milk somatic cells are a suitable substitute for documenting treatment effects of dietary oils on gene expression in goat mammary tissue.