Several long-chain fatty acids (LCFA) are natural ligands of nonruminant peroxisome proliferator-activated receptor-gamma (PPARG), which, along with its lipogenic target genes, is upregulated in bovine mammary tissue during lactation. Thus, PPARG might represent an important control point of bovine milk fat synthesis. We tested lipogenic gene network expression via quantitative PCR of 19 genes in bovine mammary epithelial cells cultured with 16:0, 18:0, cis-9 18:1, trans-10 18:1, trans-10,cis-12 18:2 [t10c12 conjugated linoleic acid (CLA)], 20:5, ethanol (control), and the PPARG agonist rosiglitazone (ROSI). Triplicate cultures were maintained for 12 h with 50 muM ROSI or 100 muM LCFA. Responses common to 16:0 and 18:0 relative to the control included significantly greater expression of INSIG1 (+298%, +92%), AGPAT6 (+137%, +169%), FABP3 (+755%, +338%), and FABP4 (+171%, 157%). These were coupled with greater intracellular lipid droplet formation and mRNA of ACSS2, LPIN1, SCD, and SREBF2 in response to 16:0, and greater DGAT1 and THRSP with 18:0. Trans-10 18:1 and t10c12 CLA reduced expression of FASN (-60%, -31%), SCD (-100%, -357%), and SREBF1 (-49%, -189%). Furthermore, t10c12 CLA downregulated ACSS2, FABP3, INSIG1, SREBF2, and THRSP expression. Expression of SREBF1 was lower with cis-9 18:1 (-140%) and 20:5 (-125%) compared with the control. This latter LCFA also decreased SCD, SREBF2, and LPL expression. No effects of LCFA or ROSI on PPARG were observed, but ROSI upregulated (+39% to +269%) expression of ACACA, FASN, LPIN1, AGPAT6, DGAT1, SREBF1, SREBF2, and INSIG1. Thus, these genes are putative PPARG target genes in bovine mammary cells. This is the first report showing a direct effect of trans-10 18:1 on bovine mammary cell lipogenic gene expression. The coordinated upregulation of lipogenic gene networks in response to ROSI and saturated LCFA offers support for PPARG activation in regulating bovine milk fat synthesis.

The objectives of the present study were to examine the effect of a milk fat-depressing (MFD) diet on: 1) the activity of mammary acetyl-CoA carboxylase (ACC) and fatty acid synthase (FAS), 2) ACC mRNA relative abundance and 3) distributions of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA) in milk fat. Twelve lactating Holstein cows were used in a single reversal design. Two diets were fed: a control diet (60:40% forage/concentrate) and an MFD diet (25:70% forage/concentrate, supplemented with 5% soybean oil). The MFD diet decreased (P: < 0 0.001) milk fat by 43% and ACC and FAS activity by 61 and 44%, respectively. A reduced ACC mRNA relative abundance (P: < 0.001) corresponded with the lower ACC activity. The fatty acids synthesized de novo were decreased (P: < 0. 002), whereas tFA were increased from 1.9 to 15.6% due predominantly to a change in trans-10-18:1 isomer (P: < 0.001). With the MFD diet, the trans-7, cis-9 and trans-10, cis-12 CLA isomers were elevated (P: < 0.001), in contrast to the decrease in trans-11-18:1 (P: < 0. 001) and cis-9, trans-11-18:2. The data were consistent with a dietary effect on mammary de novo FA synthesis mediated through a reduction in ACC and FAS activity and in ACC mRNA abundance. The results were compatible with a role of trans-10, cis-12 CLA in milk fat depression, but alterations noted in tFA and other CLA isomers suggest that they also may be important during diet-induced milk fat depression.

Duodenal and milk samples obtained from lactating cows in a previous study were analyzed to compare the content and isomer distribution of conjugated linoleic acids (CLA) and trans-18:1 fatty acids (tFA). Four diets containing either low [25 g/100 g dry matter (DM)] or high (60 g/100 g DM) forage were fed with or without 2% added buffer to four multiparous Holstein dairy cows in a 2 x 2 factorial, 4 x 4 Latin square design with 3-wk experimental periods. Duodenal flows of CLA were low (1.02-1.84 g/d), compared with that of tFA (57-120 g/d), regardless of diet. The greatest amounts of CLA and tFA, as well as the greatest proportions of trans-10-18:1 (P < 0.02), and cis-9, trans-11 (P < 0.01) and trans-10, cis-12 CLA (P < 0.01) were in the duodenal flow of cows fed the low forage unbuffered diet. In milk fat, tFA were increased by the low forage unbuffered diet and the trans-10-18:1 (P < 0.02) replaced trans-11-18:1 as the major 18:1 isomer. Milk CLA secretion (7.2-9.1 g/d) was greater (P < 0.001) than that in the duodenal flow with each diet. This was due to the increase in cis-9, trans-11-18:2 and trans-7, cis-9 CLA, resulting most likely from endogenous synthesis via Delta9-desaturation of ruminally derived tFA. For other CLA isomers, duodenal flow was always greater than milk secretion, suggesting that they essentially were produced in the rumen.

Milk fat depression in cows fed high grain diets has been shown to be related to increased trans-C18:1 fatty acids in milk. Trans-C18:1 fatty acids are produced as a result of incomplete biohydrogenation of dietary polyunsaturated fatty acids in the rumen. The objective of this study was to determine the effects of varying amounts of dietary concentrate and buffer addition on duodenal flow, apparent absorption, and incorporation of trans-C18:1 fatty acids into milk fat. Four ruminally and duodenally cannulated multiparous Holstein cows in midlactation were fed diets consisting of 60% (high) or 25% (low) forage with or without buffer (1.5% NaHCO3 and 0.5% MgO). Treatments were arranged in a 2 x 2 factorial within a 4 x 4 Latin square design. The diet containing low forage and no buffer increased the flow of trans-C18:1 fatty acids to the duodenum compared with the effects of other diets (120 vs. 57 to 66 g/d). Ruminal pH was lower for cows fed the low forage diets. The addition of buffer increased ruminal pH by 0.19 and 0.02 units for cows fed the low forage and high forage diets, respectively. Cows fed the diet containing low forage and no buffer produced milk with a lower fat percentage. The addition of buffer to the low forage diet partially corrected milk fat depression. Milk trans-C18:1 fatty acids were higher for cows fed the low forage diet without buffer than for cows fed the other diets (5.8% vs. 3.0%). Altered ruminal function resulting from low ruminal pH for cows fed the low forage diet and no buffer may play a role in the increased production of trans-C18:1 fatty acids in the rumen.

The objective of the study was to determine the effects of dietary fat source on duodenal flow, apparent absorption, and milk fat incorporation of trans-C18:1 fatty acids. Four ruminally and duodenally cannulated multiparous Holsteins cows in mid to late lactation were fed a basal diet containing 36% corn silage, 24% alfalfa haylage, and 40% concentrate (dry matter basis). Diets contained 0% supplemental fat (control diet), 3.7% high oleic sunflower oil, 3.7% high linoleic sunflower oil, or 3.7% partially hydrogenated vegetable shortening; treatments were administered in a 4 x 4 Latin square design with 3-wk experimental periods. The flow of trans-C18:1 to the duodenum was higher for cows fed diets supplemented with fat than for cows fed the control diet (283 vs. 64 g/d). Incomplete biohydrogenation accounted for the increased flow of trans-C18:1 to the duodenum in cows fed diets containing high oleic and high linoleic sunflower oil. Increased flow of trans-C18:1 in cows fed the diet containing partially hydrogenated vegetable shortening most likely originated from the trans-C18:1 in the diet. Milk fat percentages were 3.48, 3.07, 3.18, and 3.38% for cows fed the control diet and diets containing high oleic sunflower oil, high linoleic sunflower oil, and vegetable shortening, respectively. Milk trans-C18:1 increased from 2.9 to 11.2% of the total fatty acids for cows fed the control diet and the diets supplemented with fat, respectively. Milk trans-C18:1 were equal across all diets supplemented with fat. Ruminal and total tract digestion of organic matter, neutral detergent fiber, and N did not change with fat supplementation. Results showed that trans-C18:1 is increased in the milk of cows with reduced milk fat; however, excessive amounts of trans-C18:1 in milk do not necessarily correspond directly to milk fat depression.