Effect of sunflower-seed oil or linseed oil on milk fatty acid secretion and lipogenic gene expression in goats fed hay-based diets

Abstract

Plant oils in the diet are known to alter milk fat composition owing to changes in the supply of fatty acid precursors and/or activity of lipogenic enzymes in the mammary gland. Thirteen mid-lactating Alpine goats were used in a 3 x 3 Latin square design with 28-d periods to evaluate possible mechanisms regulating milk fat synthesis and fatty acid composition on grass hay-based diets containing none (H) or 55 g/kg diet dry matter of sunflower-seed oil (HSO) or linseed oil (HLO). Inclusion of oils in the diet had no effect on milk yield but enhanced (P<0.05) milk fat secretion. Compared with the control, HLO and HSO decreased (P<0.05) C10-C16 secretion and increased (P<0.05) C18 output in milk, responses that were accompanied by reductions in milk fat cis-9 14:1/14:0, cis-9 18:1/18:0 and cis-9, trans-11 18:2/cis-9 18:1 concentration ratios. Plant oil supplements decreased (P<0.05) mammary stearoyl-CoA desaturase (SCD) activity but had no effect on SCD mRNA. Treatments had no effect on glucose-6-phosphate dehydrogenase, malic enzyme and glycerol-3-phosphate dehydrogenase activity, or mRNA abundance and/or activity of lipoprotein lipase, acetyl-CoA carboxylase and fatty acid synthase in mammary, hepatic or adipose tissue. The results provided little support for milk fatty acid secretion responses to HLO and HSO being mediated via changes in mammary, hepatic or adipose mRNA abundance or in the activity of key lipogenic enzymes. In conclusion, plant oils in the diet enhance milk fat synthesis, alter milk fatty acid composition and specifically inhibit mammary SCD activity in the goat. Furthermore, the results suggest that the regulation of mammary lipogenesis in response to plant oils appears related to factors other than altered mammary gene expression or potential lipogenic enzyme activity.

Role of trans fatty acids in the nutritional regulation of mammary lipogenesis in ruminants

“…Indirect comparisons between species indicate that the reductions in milk 10:0 to 16:0 output in goats fed grass hay based diets supplemented with linseed oil (Bernard et al, 2009b) or maize-silage-based diets supplemented with sunflower-seed oil (Bernard et al, 2009a) of 27% and 32%, respectively, are lower than corresponding decreases of 46% and 69% reported in cows fed diets of similar composition . Feeding diets that cause MFD Ahnadi et al, 2002; or administration of trans-10, cis-12 CLA at the abomasum (Baumgard et al, 2002) or intravenously Gervais et al, 2009) results in 30% to 59% decreases in the output of 4:0 to 16:0 in milk that are associated with a decrease in mammary ACACA and FASN mRNA abundance and/or activity of the transcribed proteins in cows.…”

“…Similarly, administration of trans-10, cis-12 CLA at the duodenum was reported to lower milk fat desaturase ratios in the absence of significant changes in milk fat secretion in goats (Andrade and Schmidely, 2006). In some experiments with goats, lipid supplements in the diet have been shown to reduce milk fat desaturase ratios but to have no effect on SCD activity (Bernard et al, 2008(Bernard et al, , 2009a(Bernard et al, , 2009b(Bernard et al, and 2009c. It is possible that milk fat desaturase ratios are regulated by factors other than SCD activity, including differential uptake, turnover and utilization of fatty acid substrates in mammary tissue.…”

“…Feeding diets that cause MFD Ahnadi et al, 2002; or administration of trans-10, cis-12 CLA at the abomasum (Baumgard et al, 2002) or intravenously Gervais et al, 2009) results in 30% to 59% decreases in the output of 4:0 to 16:0 in milk that are associated with a decrease in mammary ACACA and FASN mRNA abundance and/or activity of the transcribed proteins in cows. In goats, diets causing 18% to 32% decreases in the output of fatty acids synthesized de novo in milk do not result in significant changes in mammary ACACA or FASN expression or ACC and FAS activity (Bernard et al, 2005b(Bernard et al, , 2009a(Bernard et al, and 2009b. Mammary abundance of ACACA and FASN mRNA in the bovine and caprine is known to be positively related with the output of 4:0 to 16:0 in milk (Bernard et al, 2008) suggesting that variation in the expression of ACACA and FASN is an important component in the regulation of de novo fatty acid synthesis in both ruminant species.…”

“…Recent studies also indicate that intravenous administration of trans-10, cis-12 CLA has no effect on mammary SCD5 expression in lactating cows (Gervais et al, 2009). Experiments in goats have shown that supplementing diets based on grass hay with OA enriched sunflower-seed oil (Bernard et al, 2005b), sunflower-seed oil or linseed oil decreases SCD activity (Bernard et al, 2009b) but has no effect on mammary SCD transcript abundance. In contrast, inclusion of sunflower-seed oil and linseed oil in maize silage-based diets was reported to have no effect on SCD mRNA or activity in caprine mammary tissue (Bernard et al, 2009a).…”

“…Several experiments in goats have provided evidence to support the involvement of post-translational mechanisms in the regulation of SCD activity in ruminants. Inclusion of cis-9 18:1 enriched sunflower oil (Bernard et al, 2005b), sunflower oil or linseed oil (Bernard et al, 2009b) in the diet of goats fed grass hay-based diets has been shown to lower mammary SCD activity measured ex vivo but have no effect on mammary SCD mRNA abundance.…”