Effects of different model diets on milk composition and expression of genes related to fatty acid synthesis in the mammary gland of lactating dairy goats

This study examined the effects of different roughage diets on milk composition and the expression of key genes associated with fatty acid (FA) synthesis in the mammary gland of lactating dairy goats. Eight multiparous lactating goats (body weight = 43.6 ± 2.5 kg, 90 ± 12 d in milk) fitted with external pudic artery and subcutaneous abdominal vein catheters were assigned to 2 treatments in a crossover design. The goats were fed different roughage diets with a similar concentrate-to-roughage ratio. The diets were (1) a high-quality roughage treatment (HQR) containing 28.5% Chinese wildrye hay, 19% corn silage, 9.5% alfalfa, and 43% concentrate or (2) a low-quality roughage treatment (LQR) containing 28% Chinese wildrye hay, 28% corn stover, and 44% concentrate, on a dry matter basis. Each feeding period lasted 21 d. The first 18 d served as an adaptation period, and the last 3 d served as a sample collection period. Dry matter intake, milk yield, and milk composition were measured. Milk and blood samples were collected for FA analysis. Mammary gland biopsies were performed after milking on the last day of each period and the tissues were analyzed for the mRNA expression of acetyl-coenzyme A carboxylase-α (ACACA), FA synthase (FASN), stearoyl CoA desaturase (SCD), and lipoprotein lipase (LPL). Dry matter intake and milk yield were not affected by the treatments. Milk fat (3.16 vs. 2.96%) and protein (2.99 vs. 2.89%) contents were higher in HQR goats than in LQR goats, and milk fat yield tended to be higher in HQR goats (16.7 vs. 15.1 g/d). Milk FA composition was not different between treatments, except for C18:3n-3 (0.27 vs. 0.15 g/100 g). Compared with LQR goats, HQR goats had a higher vein concentration of total FA (0.62 vs. 0.44 mg/mL). In HQR goats, the mammary balance of total FA increased (9.17 vs. 5.51 g/d), whereas the clearance rate of total FA decreased (103.03 vs. 138.25 L/d). No differences were found in mammary blood flow, artery concentration, and mammary uptake of FA between treatments. Compared with LQR, the expression of FASN and ACACA tended to be increased by 20 and 18%, and the expression of LPL and SCD were increased by 39 and 50% in HQR, respectively. The results demonstrated that diets with HQR can increase milk fat content and yield as well as the expression of LPL and SCD in the mammary gland of dairy goats.