Effects of intravenous infusion of trans-10, cis-12 18:2 on mammary lipid metabolism in lactating dairy cows

Abstract

It has previously been established that supplementation of trans-10, cis-12 18:2 reduces milk fat content and fat deposition in several species. The objectives of the study were 1) to examine whether potential mechanisms by which trans-10, cis-12 18:2 is reported to affect lipid metabolism in adipose tissue of different species could be partly responsible for the inhibition in milk fat synthesis in lactating dairy cows; and 2) to investigate the effects of trans-10, cis-12 18:2 on the expression of a newly identified isoform of stearoyl-coenzyme A desaturase (SCD) in bovine mammary tissue. Four primiparous Holstein cows in established lactation, fitted with indwelling jugular catheters, were used in a balanced 2 x 2 crossover design. For the first 5 d of each period, cows were infused intravenously with a 15% lipid emulsion providing 10 g/d of either cis-9, cis-12 18:2 (control) or trans-10, cis-12 18:2 (conjugated linoleic acid; CLA). On d 5 of infusion, mammary gland biopsies were performed and tissues were analyzed for mRNA expression of acetyl-coenzyme A carboxylase, fatty acid synthetase, lipoprotein lipase, SCD1, SCD5, sterol regulatory element-binding protein-1, IL6, IL8, and tumor necrosis factor-alpha by real-time PCR. Compared with the control treatment, CLA reduced milk fat concentration and yield by 46 and 38%, respectively, and increased the trans-10, cis-12 18:2 content in milk fat from 0.05 to 3.54 mg/g. Milk yield, milk protein, and dry matter intake were unaffected by treatment. Infusion of the CLA treatment reduced the mRNA expression of acetyl-coenzyme A carboxylase and fatty acid synthetase by 46 and 57%, respectively, and tended to reduce the expression of SCD1 and lipoprotein lipase. Abundance of mRNA for sterol regulatory element-binding protein-1 was reduced by 59% in the CLA treatment group. However, infusing trans-10, cis-12 18:2 did not affect the expression of transcripts for SCD5, tumor necrosis factor-alpha, IL6, and IL8. Results from the current study corroborate the idea that effects of trans-10, cis-12 18:2 reported on adipose tissue in animal models and humans are not part of the response in the inhibition of milk fat synthesis in lactating dairy cows. They also support the hypothesis that SCD1 and SCD5 present important differences in their regulation and physiological roles.

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. 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.…”

“…Studies in cows have shown that feeding high concentrate diets containing sunflower oil or fish oil and soya bean oil and causing MFD is not associated with altered mammary SCD mRNA abundance. However, expression of SCD in the bovine mammary gland has been shown to be significantly downregulated in response to dietary supplements of rumen protected fish oil (Ahnadi et al, 2002) or following abomasal (Baumgard et al, 2002) or intravenous (Gervais et al, 2009) infusions of trans-10, cis-12 CLA. 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).…”

“…However, expression of SCD in the bovine mammary gland has been shown to be significantly downregulated in response to dietary supplements of rumen protected fish oil (Ahnadi et al, 2002) or following abomasal (Baumgard et al, 2002) or intravenous (Gervais et al, 2009) infusions of trans-10, cis-12 CLA. 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 vivo (Baumgard et al, 2002;Gervais et al, 2009) and in vitro (Peterson et al, 2004;Kadegowda et al, 2009) studies indicate that trans-10, cis-12 CLA decreases SCD transcription in the bovine. 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).…”

“…Several studies have demonstrated the involvement of SREBP1 and/or PPAR during diet-induced changes in mammary lipogenic gene expression in lactating cows (Peterson et al, 2004;Bionaz and Loor, 2008b), or in response to 3-to 5-day intravenous infusions of trans-10, cis-12 CLA Gervais et al, 2009) with the implication that these transcription factors are central elements in the overall regulation of milk fat synthesis. Two isoforms of SREBP1 (a and c) can be differentially expressed in various tissues.…”