Effects of polyunsaturated fatty acids from plant oils and algae on milk fat yield and composition are associated with mammary lipogenic and SREBF1 gene expression

Abstract

The main aim of the present study was to examine the effects of long-term supplementing diets with saturated or unprotected polyunsaturated fatty acids from two different plant oils rich in either n-3 or n-6 fatty acids (FAs) plus docosahexaenoic acid (DHA)-rich algae on mammary gene expression and milk fat composition in lactating dairy cows. Gene expression was determined from mammary tissue and milk epithelial cells. Eighteen primiparous German Holstein dairy cows in mid-lactation were randomly assigned into three dietary treatments that consist of silage-based diets supplemented with rumen-stable fractionated palm fat (SAT; 3.1% of the basal diet dry matter, DM), or a mixture of linseed oil (2.7% of the basal diet DM) plus DHA-rich algae (LINA; 0.4% of the basal diet DM) or a mixture of sunflower oil (2.7% of the basal diet DM) plus DHA-rich algae (SUNA; 0.4% of the basal diet DM), for a period of 10 weeks. At the end of the experimental period, the cows were slaughtered and mammary tissues were collected to study the gene expression of lipogenic enzymes. During the last week, the milk yield and composition were determined, and milk was collected for FA measurements and the isolation of milk purified mammary epithelial cells (MECs). Supplementation with plant oils and DHA-rich algae resulted in milk fat depression (MFD; yield and percentage). The secretion of de novo FAs in the milk was reduced, whereas the secretion of trans-10,cis-12-CLA and DHA were increased. These changes in FA secretions were associated in mammary tissue with a joint down-regulation of mammary lipogenic enzyme gene expression (stearoyl-CoA desaturase, SCD1; FA synthase, FASN) and expression of the regulatory element binding transcription factor (SREBF1), whereas no effect was observed on lipoprotein lipase (LPL) and glycerol-3-phosphate acyltransferase 1, mitochondrial (GPAM). A positive relationship between mammary SCD1 and SREBF1 mRNA abundances was observed, suggesting a similar regulation for these genes. Such data on mammary gene expression in lactating cows presenting MFD contribute to strengthen the molecular mechanisms that govern milk fat synthesis in the mammary glands. In purified MEC, the dietary treatments had no effect on gene expressions. Differences between mammary tissue and milk purified MEC gene expression were attributed to the effect of lipid supplements on the number of milk purified MEC and its RNA quality, which are determinant factors for the analysis of gene expression using milk cells.

mRNA abundance of genes involved in mammary lipogenesis during fish oil- or trans-10,cis-12 CLA-induced milk fat depression in dairy ewes

“…Indeed, SREBF1 is a central regulator of milk fat synthesis and its role in MFD appears crucial (Bernard et al, 2008;Bauman et al, 2011;Bionaz et al, 2015). Therefore, the lack of variation in its mRNA abundance in FO and CLA treatments was unexpected and contrasts with most reports on MFD in lactating ruminants (Angulo et al, 2012;Carreño et al, 2016 and MFD, as mRNA abundances in FO and CLA were not statistically different from those in the control. Nevertheless, significant variations between FO and CLA treatments in this transcription factor and the fact that it codes for a SREBP1 regulatory protein (Bauman et al, 2011;Bionaz et al, 2015) 1 SED = standard error of the difference.…”

Comparison of mammary lipid metabolism in dairy cows and goats fed diets supplemented with starch, plant oil, or fish oil

“…Similarly, the supplements of FO in the present study lowered milk fat content in cows (−31%; Toral et al, 2015) and had no or little effect on mammary mRNA and enzyme activities. These data are not consistent with the reported decreasing effects of diets containing FO (Ahnadi et al, 2002;Harvatine and Bauman, 2006) or the combination of plant oil and algae (Angulo et al, 2012) on mammary mRNA abundance of lipogenic genes in cows and milk fat content (−34% in Ahnadi et al, 2002; −31% in Harvatine and Bauman, 2006;and −39% in Angulo et al, 2012).…”

“…Regarding the methodology for the measurement of mRNA abundance on mammary tissue collected by biopsy, the same method was used in the present study in cows and in Angulo et al (2012) on tissue collected at slaughter from cows fed a combination of plant oil and algae, where effects on mammary mRNA abundance were reported. When considering the time of sampling relative to milking and the last meal, in most of the abovementioned studies this information was not available except in Harvatine and Bauman (2006), which specified that cow mammary biopsies were collected using a Bard biopsy system at 1 to 3 h after milking and with diets consumed ad libitum, suggesting free access to the TMR.…”

Effect of incremental amounts of camelina oil on milk fatty acid composition in lactating cows fed diets based on a mixture of grass and red clover silage and concentrates containing camelina expeller

“…Milk fat concentration ratios of product to substrate for SCD1 were marginally decreased in response to CO. Part of the decrease may reflect a higher availability of PUFA at the mammary gland inhibiting SCD1 activity (Chilliard et al, 2000). Several biohydrogenation intermediates including trans-10,cis-12 CLA, trans-10,trans-12 CLA, and trans-9,trans-11 CLA in addition to 20-and 22-carbon n-3 FA are thought to lower SCD1 activity in the bovine mammary gland (Angulo et al, 2012). In the present study, the concentration of these CLA isomers in milk fat declined linearly in response to CO supplementation, but 3.2-and 2.7-fold linear increases in milk fat cis-11,cis-14,cis-17 20:3 and cis-13,cis-16,cis-19 22:3 concentrations, respectively, were detected.…”

“…In cows, mammary SCD1 gene expression and the concentration ratio of cis-9,trans-11 CLA to trans-11 18:1 in milk has been found to decrease in response to linseed oil (mean ratio 0.31) or linseed and DHA-enriched algae (0.16) compared with the same diet containing saturated FA from palm oil (0.41; Angulo et al, 2012). It therefore appears unlikely that dietary supplements of CO have a substantive negative effect on mammary SCD1 activity, with the implication that the majority of cis-9,trans-11 CLA in milk on all experimental diets originates from desaturation of trans-11 18:1 in the mammary gland.…”