Diet-Induced Milk Fat Depression in Dairy Cows Results in Increased trans-10, cis-12 CLA in Milk Fat and Coordinate Suppression of mRNA Abundance for Mammary Enzymes Involved in Milk Fat Synthesis

Abstract

Milk composition can be altered by diet, and one example is milk fat depression (MFD) in dairy cows. The biohydrogenation theory of MFD has implicated unique fatty acids formed by altered rumen biohydrogenation of PUFA; one example is trans-10, cis-12 conjugated linoleic acid (CLA). In the present study, we induced MFD with a high concentrate/low forage (HC/LF) diet and examined milk composition, milk fatty acid changes and mammary lipogenic mRNA abundance to determine the mechanism involved. The HC/LF diet reduced milk fat percentage by 25% and yield by 27% with no effect on dietary intake, milk production, protein or lactose. Milk fatty acids synthesized de novo in the mammary gland and fatty acids taken up from circulation were reduced to a similar extent (molar basis). MFD was also characterized by the appearance of trans-10, cis-12 CLA in the milk fat. We analyzed mammary mRNA abundance for lipogenic genes and detected reductions for acetyl CoA carboxylase (ACC), fatty acid synthase (FAS), fatty acyl CoA ligase, glycerol phosphate acyltransferase (GPAT) and acylglycerol phosphate acyltransferase (AGPAT). There was no effect on the milk protein gene, kappa-casein. The reductions in mRNA were also correlated with the appearance of trans-10, cis-12 CLA in the milk fat for ACC, FAS, lipoprotein lipase and GPAT. This study demonstrates that diet-induced MFD involves coordinated effects on mRNA for mammary lipid synthesis pathways, and provides support for a mechanism involving alterations in transcriptional activation of these genes.

Recent advances in the regulation of milk fat synthesis

“…Mammary lipogenic capacity may be regulated at multiple levels including transcription, translation, protein turnover and enzyme activity. Decreased mammary expression of genes for key enzymes and proteins involved in FA uptake, synthesis, transport and esterification occurred during both diet-and CLA-induced MFD (Piperova et al, 2000;Ahnadi et al, 2002;Baumgard et al, 2002b;Peterson et al, 2003;. Combined, these observations define MFD as a decreased mammary capacity for lipid synthesis due to a coordinated transcriptional down-regulation of enzymes and proteins involved in milk fat synthesis.…”

“…The milk fat concentration of trans-10, cis-12 CLA is linearly related to the abomasally administered dose, and milk fat trans-10, cis-12 CLA concentration is curvilinearly related to the decrease in milk fat yield during abomasal infusion (de Veth et al, 2004). Therefore, milk fat trans-10, cis-12 CLA concentration can be used to predict the expected extent of MFD contributable to the trans-10, cis-12 CLA isomer during dietinduced MFD (Peterson et al, 2003). Although there is a relationship between milk fat concentration of trans-10, cis-12 CLA and milk fat yield during diet-induced MFD, it is clear this CLA isomer only accounts for a modest portion of the MFD observed during most diet-induced MFD conditions (Peterson et al, 2003;Griinari and Bauman, 2006;Shingfield et al, 2008a).…”

“…Therefore, milk fat trans-10, cis-12 CLA concentration can be used to predict the expected extent of MFD contributable to the trans-10, cis-12 CLA isomer during dietinduced MFD (Peterson et al, 2003). Although there is a relationship between milk fat concentration of trans-10, cis-12 CLA and milk fat yield during diet-induced MFD, it is clear this CLA isomer only accounts for a modest portion of the MFD observed during most diet-induced MFD conditions (Peterson et al, 2003;Griinari and Bauman, 2006;Shingfield et al, 2008a). Furthermore, there is often little or no change in trans-10, cis-12 CLA in the milk fat when MFD is induced by feeding fish oils (reviewed by Shingfield and Griinari, 2007).…”

The effect of fish oil supplementation of pregnant and lactating ewes on milk production and lamb performance

“…The phenomenon of milk fat depression (MFD) induced by PUFA supplementation of lactating ruminants has been reviewed in detail (Peterson et al, 2003;Bauman et al, 2006) and it is clear that specific fatty acids produced as intermediates during ruminal biohydrogenation of C 18:2 (n-6) play a significant role in reducing milk fat synthesis through inhibitory effects on mammary gene expression (Peterson et al, 2003). This mechanism would explain the 27% decrease in milk fat concentration conferred by fish oil supplementation, and, in combination with effects of diet upon milk yield, the 29% decrease in milk fat yield.…”

Effect of silage type and concentrate level on conjugated linoleic acids, trans-C18:1 isomers and fat content in milk from dairy cows

“…However, diets that provide large amounts of readily digestible carbohydrates such as starch, with [4,5] or without [6,7] a supplement of vegetable oil often lead to increased proportions of trans10-C18:1 and trans10,cis12-CLA in milk fat. This response is usually caused by a decline in rumen pH [4,6] and shifts in the bacterial populations [8] whereby the biohydrogenation pathway of C18:2n−6 is altered [9].…”