Effects of essential oils supplementation on in vitro and in situ feed digestion in beef cattle

The objective of this study was to investigate the effect of lemongrass oil (LMO) and a mixture of garlic and ginger oil (CEO) on gas production (GP) and feed digestibility using the batch culture and in situ ruminal technique. Four feeds: wheat distillers dried grains with solubles (DDGS), barley grain, grass hay, and a total mixed ration (TMR) were tested with varying essential oil (EO) dosages. The TMR consisted of 350 g/kg grass hay, 150 g/kg alfalfa hay, 200 g/kg barley grain, 100 g/kg corn DDGS, 100 g/kg wheat DDGS, 50 g/kg canola meal, and 50 g/kg vitamin and mineral supplement. The in vitro study was a complete randomized design with 2 × 4 factorial arrangement of two EO (LMO and CEO) combined with four dosages of EO (i.e., 0, 100, 200, and 300 mg/kg substrate DM). Digestibilities of DM (DMD) and neutral detergent fibre (NDFD) were measured at 24 h and 48 h post incubation, while GP was read at 3, 6, 12, 24, 36, and 48 h post incubation. In situ ruminal degradability was measured using three ruminally fistulated beef heifers with incubation time of 4, 12, 24 or 48 h. There was no interaction on in vitro DMD and NDFD between EO source and its dose. The DMD and NDFD were greater with CEO compared to LMO for wheat DDGS (P < 0.01; 48 h) and barley grain (P < 0.01; 24 h), but lower for TMR (P < 0.05; 24 or 48 h). Increasing the dosage of EO linearly (P < 0.01) increased the DMD of wheat DDGS and barley grain at 24 h post incubation, and linearly (P < 0.01) and quadratically (P < 0.05) improved in vitro DMD and NDFD of grass hay and TMR with addition of LMO and CEO at 24 or 48 h post incubation. The cumulative GP was overall affected (P < 0.01) by both LMO and CEO in quadratic manner after 24, 36 or 48 h of incubation. In situ ruminal DMD of wheat DDGS and barley grain were higher (P < 0.05) at 4 or 24 h of incubation with CEO than with control or LMO which had no differences in DMD. However, the in situ DMD of grass hay and TMR were improved by both LMO and CEO supplementation after 24 h (P < 0.01) or 48 h (P < 0.05) post incubation. The dose of 200 mg/kg DM was likely cost-effective to improve DMD for both LMO and CEO. The LMO and CEO appeared to be more effective to improve the DMD of fibrous feeds since the in vitro DMD and NDFD of grass hay and TMR were consistently improved at 24 h or 48 h post incubation. These results suggested that the LMO and CEO used in the present study could be potentially developed as rumen modifier to improve feed digestibility in the rumen.