The Effects of a Hyperinsulinemic-Euglycemic Clamp on Milk Fat Synthesis and the Expression of Fat Synthesis-Related Genes in the Mammary Gland Tissues of Lactating Goats

To determine whether insulin exerts an effect on milk fat yield through the direct regulation of milk fat synthesis in the mammary gland, the hyperinsulinemic-euglycemic clamp procedure was performed in lactating goats in the present study. The effects of the hyperinsulinemic-euglycemic clamp on milk yield, milk composition, milk fatty acid yield and the expression levels of mRNAs of milk fat synthesis-related genes were examined. The results revealed that the hyperinsulinemiceuglycemic clamp had no significant effect on the milk yield, the milk protein yield, the yield and content of lactose or the yield and content of solids-not-fat (SNF) (P > 0.05). In contrast, the milk fat percentage and milk fat yield were decreased by 35.3% and 33.6%, respectively (P < 0.01). Among the 19 fatty acids examined, the yields of 9 fatty acids were significantly reduced (P < 0.05) following the clamp procedure, including C16:0 (hexadecanoic acid), 3 fatty acids derived from blood (>C16) and 5 fatty acids synthesized de novo in the mammary gland ( 0.05), including acetyl-coenzyme A carboxylase (ACC), fatty acid synthase (FAS), fatty acidbinding protein (FABP), lipoprotein lipase (LPL), stearoyl-CoA desaturase (SCD) and glycerol-3-phosphate acyltransferase (GPAT). However, the expression level of the SCD gene was significantly reduced during the post-procedure period (P < 0.05) but returned to a normal level at 48 h after termination of the clamp procedure. It was concluded that the hyperinsulinemic-euglycemic clamp exerted a direct effect on milk fatty acid desaturation.