Effect of different dietary fats on protein expression of sterol regulatory element-binding protein 1 (SREBP-1) in mammary gland tissue of lactating cows

Abstract

The present study investigated the effect of three different dietary fats [saturated fat (SAT) (3.1% TMR DM); linseed oil (LINA) (2.7% TMR DM) or sunflower oil (SUNA) (2.7% TMR DM) added with docosahexaenoic acid rich algae (0.4% TMR DM)] on SREBP-1 protein expression in mammary gland tissue of German Holstein cows (n=18) in the context of milk yield, milk fat content and milk fatty acid composition. Prerequisite for this investigation was the development of a Western blot methodology adapted for bovine mammary gland tissue using two different primary antibodies to specifically detect and differentiate between precursor (pSREBP-1, 125kDa) and transcriptionally active SREBP-1 (mSREBP-1, 68kDa).Upon a ten-week feeding intervention, significantly reduced milk fat contents, total saturated fatty acid amounts and single saturated fatty acid concentrations (C10:0, C12:0, C14:0, C16:0) were obtained in LINA and SUNA group, whereas milk yields did not substantially differ between feeding groups. The assumption that the effects of plant oil/DHA rich algae supplementation on milk fat composition were mediated by shifted SREBP-1 protein expression were only confirmed in regard to slightly reduced protein expression levels of pSREBP-1 in SUNA group tissue samples (P=0.087), whereas similar protein expression levels of transcriptionally active mSREBP-1 were found in SAT, LINA and SUNA group.