RESUMO
The efficacy of conjugated linoleic acid (CLA) in diet supplements for milk fat reduction is well documented in several species. However, the mechanisms by which fatty acids regulate mammary lipogenesis remain largely unknown, especially with regard to gene expression of enzyme and regulators. In this study, 8 Holstein dairy cows in their mid-lactation period were randomly divided into 2 groups. Control cows received a Ca salt of palm oil fatty acid dietary supplement, and those in the CLA group were fed Ca salts of CLA (Ca-CLA), all in a dose of approximately 200 gâcow(-1)âday(-1) for 14 days. The milk yield was recorded daily, and protein, lactose, and fat in the milk were quantified every 3 days for 2 weeks. Fatty acids in the milk were analyzed with gas-liquid chromatography. Measurement of messenger RNA levels of the main lipogenic genes of lipoprotein lipase, acetyl-coenzyme A (CoA) carboxylase, fatty acid synthase, stearoyl-CoA desaturase, and transcription factors such as sterol response element binding protein 1 (SREBP1) and peroxisome proliferator-activated receptor γ was performed in biopsy samples of mammary tissue on the last day. The results indicated that dietary Ca-CLA caused a continuous reduction of milk fat (P < 0.01) with no effect on milk yield, milk protein, and lactose. The fatty acid profile in the milk from the CLA group differed from that from controls, and the yield of milk fatty acid decreased (P < 0.01) with Ca-CLA supplementation. The depressed expression of lipogenic genes (lipoprotein lipase, acetyl-CoA carboxylase, fatty acid synthase, and stearoyl-CoA desaturase) demonstrated inhibition of fatty acid de novo synthesis and uptake in the mammary gland of the CLA group. Furthermore, the gene expression of transcription factor SREBP1 was also downregulated (P < 0.01), but peroxisome proliferator-activated receptor γ was unchanged, suggesting that SREBP1 may play a key role in the regulation of lipogenic gene expression in the lactating mammary gland.