EFFECT OF FORAGE LEVEL AND OIL SUPPLEMENTATION ON FERMENTATION, TRANS FATTY ACIDS PRODUCTION AND RUMINAL BACTERIA

Conjugated linoleic acids (CLA) are unique group of trans fatty acids formed during the biohydrogenation (BH) of unsaturated fatty acids by rumen microorganisms. The reported health benefits of CLA in recent human studies have increased researchers\u27 interest in enhancing their concentrations in ruminants dairy and meat products. Despite the great successes seen in increasing milk CLA by dietary means, little information has been presented about the effect of CLA-enhancing diets on rumen microorganisms, particularly bacterial species involved in the BH process. Identifying the rumen bacteria responsible for the formation of the beneficial trans fatty acids in the rumen may provide an opportunity to isolate and grow such bacteria in vitro and then feed as a microbial supplement to dairy cows to enhance the CLA content in their milk. Therefore, the main objective of this research is to investigate how dietary forge level and oil supplementation affects trans fatty acids formation and selected strains of ruminal bacteria believed to be involved in BH. The effects of forage level and oil supplementation on fermentation, trans fatty acids and ruminal bacteria were investigated in continuous culture fermenters system. Four continuous culture fermenters were used in 4 ×x 4 Latin square design with a 2 ×x 2 factorial arrangement over four 10-d consecutive periods. The experimental diets used in this study were: 1) high forage diet (70:30 forage to concentrate (DM basis); HFC), 2) high forage plus oil supplement (HFO), 3) low forage diet (30:70 forage to concentrate; LFC), and 4) low forage plus oil supplement (LFO). The oil supplement was a blend of fish oil (FO) and soybean oil (SBO) added at 1 and 2 g/100g DM, respectively. On day 10 of each period, samples were collected from each fermenter at 3 h post morning feeding for volatile fatty acids (VFA) and fatty acids analysis using gas chromatography and for microbial analysis using real time PCR (rPCR). Fermenters pH averaged 6.5 ±± 0.05 and 5.8 ±± 0.05 with the high and low forage diets, respectively and was not affected (P \u3e 0.05) by oil supplement. Total VFA concentration was not affected by forage level (P \u3e 0.05) but decreased (P \u3c 0.05) with oil supplementation. The concentration (mM) of acetate was greater (P \u3c 0.05) with the high forage diets while the concentration of propionate was greater (P \u3c 0.05) with the low forage diet and both decreased (P \u3c 0.05) with oil supplementation. Dietary forage level had no effect (P \u3e 0.05) on butyrate concentration but oil supplementation reduced (P \u3c 0.05) concentration particularly when added with the high forage diet (P \u3c 0.02). The concentrations of trans-11 C18:1 (vaccenic acid; VA) and cis-9 trans-11 CLA were greater (P \u3c 0.01) with the high than the low forage diets and concentrations increased (P \u3c 0.01) with oil supplementation particularly when added with the high forage diet (P \u3c 0.01). The concentrations of trans-10 C18:1 and trans-10 cis-12 CLA were greater (P \u3c 0.05) with the low the high forage diets and concentrations increased (P \u3c 0.01) with oil supplementation particularly when added with the low forage diet (P \u3c 0.02). The concentration of C18:0 was greater (P \u3c 0.01) with the high than the low forage diets and oil supplementation decreased (P \u3c 0.02) C18:0 concentration in the high forage diet but increased it (P \u3c 0.01) in the low forage diet. Forage level and oil supplementation had no effect (P \u3e 0.05) on the DNA abundance of Butyrivibrio SA subgroup. The DNA abundances of Butyrivibrio fibrisolvens, Ruminococcus albus, Ruminococcus flavefaciens, Butyrivibrio VA subgroup, Anaerovibrio lipolytica and Butyrivibrio proteoclasticus were greater (P \u3c 0.05) with the high than the low forage diets. Oil supplementation reduced the DNA abundances only for R. flavefaciens, B. fibrisolvens and R. albus especially when added with the high forage diet. Results from this study may suggest that the greater trans fatty acids formation seen with the high forage diets may be related to greater activity of Butyrivibrio VA subgroup, B. fibrisolvens, R. flavefaciens, and R. albus bacteria and both Butyrivibrio SA subgroup and B. proteoclasticus seems to play a minor role in the production of C18:0 from trans C18:1. Further research is needed to identify the strain(s) of bacteria responsible for trans C18:1 reductions to C18:0, particularly under high rumen pH conditions