Context Ensiling is commonly used to conserve tropical grasses, but low water-soluble carbohydrates content and high moisture content in the grass impair silage fermentation characteristics. Essential oils may be used as silage additives to decrease fermentative losses and improve the nutritional value of silage, and aerobic stability, and in vitro DM disappearance. Aims. The present study aimed to evaluate the effect of including lemongrass essential oil (LEO) on the fermentative characteristics, fermentative losses, chemical composition, in vitro disappearance and aerobic stability of Mombasa grass (Megathyrsus maximum) silage. Methods. Mombasa grass was ensiled for 60 days in 32 experimental silos (15-L plastic buckets, 28 cm diameter and 25 cm high), in a randomly blocked design. LEO was included at 0.00, 0.67, 1.33 and 2.00 mL per kg of silage fresh matter. Silos were weighed every 15 days, pH and temperature were measured immediately after the silos were opened, and subsamples of silage were taken to measure the fermentative profile, composition of silage effluent, chemical composition and in vitro degradation of silage. Key results. Increasing the amount of LEO in Mombasa grass silage caused a linear reduction in ammonia-nitrogen, ethanol (P < 0.05), acid detergent fibre of silage, gas losses and silage pH after aerobic exposure. There was no impact (P > 0.05) on organic acid concentration, effluent production or DM recovery (P > 0.05). Conclusions (Tilley and Terry 1963). Adding LEO to Mombasa grass silage at up to 2.00 mL per kg fresh material (almost 7.5 mL/kg DM) reduces gas losses, ammonia-nitrogen and acid-detergent fibre concentration, and silage pH after aerobic exposure. However, it is not sufficient to improve DM recovery and in vitro disappearance of silage.
