Denovo synthesized fatty acids as regulators of milk fat synthesis

Abstract

The objectives of the dissertation research were to determine the role of <italic>denovo</italic> synthesized fatty acids (DNFA) in the regulation of milk fat synthesis. Milk fat responses to increasing amounts of short- and medium-chain fatty acids (SMCFA), added in the proportion as synthesized <italic>denovo</italic>, were studied in lactating dairy cows. The results showed a significant linear increase in milk fat concentration with SMCFA supplementation. However, milk fat yield was similar for all treatments.

A subsequent study was aimed at increasing the availability of SMCFA during <italic>trans</italic>-10, <italic>cis</italic>-12 CLA-induced milk fat depression (MFD) in lactating dairy cows to determine whether SMCFA can rescue part of CLA-induced MFD. Post-ruminal infusion of butterfat (BF) was used as a source of SMCFA. The BF treatment was compared to a mixture of fats containing only the long-chain FA (LCFA) with or without <italic>trans</italic>-10, <italic>cis</italic>-12 CLA infusion. Milk fat content and yield were significantly reduced with <italic>trans</italic>-10, <italic>cis</italic>-12 CLA. However, increased availability of SMCFA with BF infusion had no effects on milk fat yield and concentration. <italic>Trans</italic>-10, <italic>cis</italic>-12 CLA significantly reduced the mRNA expression of transcription factor <italic>SREBP-1c</italic> along with its downstream targets including <italic>ACC</italic>,<italic>FASN</italic>, <italic>LPL</italic>, <italic>SCD</italic> and <italic>AGPAT</italic>. The increased availability of SMCFA had no effect on either lipogenic gene or protein expression suggesting that nutritional manipulation was not sufficient to rescue <italic>trans</italic>-10, <italic>cis</italic>-12 CLA-induced MFD.

Finally, the effects of combination of a Rosiglitazone (ROSI), a <italic>PPAR-&#947;</italic> agonist, and <italic>trans</italic>-10, <italic>cis</italic>-12 CLA were examined on mammary and hepatic lipogenesis in lactating mice. Mammary lipogenesis was significantly reduced with <italic>trans</italic>-10, <italic>cis</italic>-12 CLA, reducing the milk fat content and mRNA expression of lipogenic transcription factors <italic>SREBP1-c</italic> and <italic>PPAR- &#947;</italic>. <italic>Trans</italic>-10, <italic>cis</italic>-12 CLA significantly increased hepatic lipid accumulation, while the mRNA expression of <italic>SREBP1-c</italic> and <italic>PPAR- &#947;</italic> were not altered. On the contrary, ROSI had no effects on mammary lipogenesis. However, ROSI significantly rescued <italic>trans</italic>-10, <italic>cis</italic>-12 CLA-induced hepatic steatosis.