| The objective of the study would investigate into the effect of docosahexaenoic acid (DHA) and linoleic acid (LA) on trans-vacceinc acid (TVA) accumulation in rumen and duodenum. These results will offer basal theory and application technology for improving ruminant product quality.In experiment 1, four ruminal cannulated beef steers fed a high forage diet (forage to concentrate ratio 65:35) were used to evaluate the regressive relationship between ruminal bacteria population by using real time quantity PCR method, rumen pH value and VFA content. Experimental period lasted 28 d with the initial 25 d for adaptation. Ruminal fluid was collected on d 26, 27 and 28 of experimental period, starting at 07:30 pre-feeding and at 11:30 and 17:30 post-feeding from the anterior, dorsal, and mid-ventral region of the rumen and pooled. Steers fed high forage diet had no significant change with time of feeding in rumen acetate, propionate and the ratio of acetate to propionate, while pH significantly decreased (P<0.05). Our study showed that there existed polynomial regression between the sum of F. succinogenes, B. fibrisolvens, R.albus number and rumen pH value (P<0.05). The relationship between F. succinogenes, B. fibrisolvens, R. albus population and VFA content was not strong (P>0.05). To some extent, pH value is more sensitive to reflect change of ruminal bacteria population compared with VFA concentration.In experiment 2, the objective of this study was to evaluate effect of combination of fish oil and sunflower oil different levels on TVA and CLA content of mixed ruminal, mixed duodenal bacteria and ruminal fluid, duodenal TVA flow and ruminal bacteria population in steers. Four steers with ruminal and duodenal fistulas were randomly assigned to control (CK, without additional oil supplement ), basal diet with 3.00% sunflower oil plus 1.00% fish oil (S3F1), 2.50% sunflower oil plus 1.50% fish oil (S2.5F1.5) or 2.00% sunflower oil plus 2.00% fish oil (S2F2) in a 4×4 Latin square in a 12-week period. All animals were fed high forage diets with forage to concentrate ratio 65:35. In contrast to CK, F. succinogenes DNA copy numbers in S3F1, S2.5F1.5 and S2F2 treatments decreased by 48%, 70% and 74%, respectively. The B. fibrisolvens DNA copy numbers reduced by 22.44%, 13.18% and 38.72% compared with CK, respectively. However, R. flavefaciens and R.albus did not change when oils were supplemented. With oil supplementation, TVA and cis9, trans11CLA in ruminal fluid increased, but they did not differ among S3F1, S2.5F1.5 and S2F2 treatments. As far as bacteria lipid was concerned, bacteria TVA increased, and they were similar between ruminal bacteria and duodenal bacteria. However, cis9, trans11CLA in duodenal bacteria was lower than that from ruminal bacteria. In contrast to CK, TVA average from S3F1, S2.5F1.5 and S2F2 treatments increased by 270%, and C18:0 reduced markedly. Blood TVA in oil supplementation was higer than those from CK. Blood cis-9, trans-11CLA was not detected in steers.In experiment 3, the object of this study was to determine the influence of dietary refined docosahexaenoic acid and refined free linoleic acid supplementation on the population of B. fibrisolvenss, F. succinogenes, R. flavefacie, and M. elsdenii strain YJ-4 in ruminal fluid, duodenal FA flow, milk composition and milk fatty acid profiles from lactating cows fed high forage diets (forage to concentrate ratio 60:40). Four lactating cows with ruminal, duodenal and ileal cannulas were randomly assigned into a 4×4 Latin square with 12-wk periods. These diets included control (CK, without oil addition), basal diet with 2.73% refined free linoleic acid (RFLA), 2.73% refined free linoleic acid plus 0.50% refined docosahexaenoic acid (RFLDA), or 0.50% refined docosahexaenoic acid (RFDA) on a DM basis. Dietary DHA and LA supplementation had not affect on acetate and propionate concentration, but they changed acetate to propionate ratio. The B. fibrisolvenss and F.succinogenes DNA copy number decreased with PUFA infusion, while M. elsdenii strain YJ-4 and B. fibrisolvens A38 populations increased. DHA and LA did not change R. flavefaciens population. The duodenal TVA flow in RFLDA treatment was enhanced by 5.37-, 0.39- and 2.37-fold compared with CK, RFLA and RFDA, respectively. The yields of milk lactose, free FA, total solids, casein and protein did not differ among four treatments. The TVA contents in RFLA, RFLDA and RFDA treatments were increased by 3.5-, 5.38- and 1.00-fold in contrast with the cows in CK. The cis9, trans11CLA content was enhanced by 3.09-, 6.63- and 1.97-fold in RFLA, RFLDA and RFDA treatments, respectively. The study indicated that duodenal VA flow and ruminal fluid bacteria population were changed through PUFA infusion alone, or using a combination of refined linoleic acid and refined DHA. Refined free linoleic acid infusion accelerated TVA and CLA accumulation of milk fat. Meantime, had positive interaction with refined docosahexaenoic acid on increase of milk TVA and CLA content.Taken together, TVA accumulation in rumen and intestine was partly due to dietary DHA and LA inhbited growth of B. fibrisolvens, B. hungatei JK684 and B. hungatei Su6, and increased population of B. fibrisolvens A38 and M.elsdenii strain YJ-4, but not entirely. Small amount DHA did not inhbited the first step of LA biohydrogenation, but large amount DHA inhibited the first and the last steps of LA biohydrogenation. DHA and LA had affection on microorganism TVA, but did not change cis9, trans11CLA content. Therefore, protozoa and bacteria play the key roles in duodenal TVA flow increase.
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