Use of essential oils for manipulation of rumen microbial fermentation using batch culture.

The objective of this study was to evaluate the effects of various levels of essential oils on feed digestibility, gas production and rumen fermentation. Two batch cultures were designed for screening various doses of each essential oil (EO). Treatments were control (CON), cinnamon oil (CIN), clove oil (CLO), garlic oil (GAR), ginger oil (GIN), and lemongrass oil (LEM). Dosages were 0, 200, 400, 800, and 1600 mg/kg DM in experiment I (1st batch) and 50, 100, 150, and 200 mg/kg DM in experiment II (2nd batch). Digestibility of DM (DMD), neutral detergent fiber and acid detergent fiber was measured at 24 h and 48 h post incubation, while gas production (GP) was read at 3, 6, 12, 24, 36, and 48 h post incubation. Experimental diet used was a dairy type ration consisting of 50% forage (35% grass hay and 15% alfalfa hay) and 50% concentrate (20% barley grain, 10% corn DDGS, 10% wheat DDGS, 5% canola meal, and 5% vitamin and mineral supplements). All essential oils could improve DM disappearance with consistent results in both experiment I and experiment II. Meanwhile, the essential oils had no effect on NDF and ADF digestibility. Total VFA concentration and individual VFA proportion in experiment I were not affected by the essential oils. However, 200 mg/kg DM of each EO increased total VFA concentration without any effect on individual VFA proportion in experiment II. Ammonia N concentration was reduced by the essential oils in both experiments I and II, confirming the effect of essential oils on deamination. However, the effect of EOs on methane production was apparently negligible. These results suggest that the EOs used in the present study could be potentially developed as rumen modifiers to improve feed digestibility in the rumen.