Use of cashew and castor essential oils to improve fibre digestibility in high forage diets: digestibility, ruminal fermentation and microbial protein synthesis

Abstract

High forage diets in the tropics are less efficient and more contaminating due to high energy losses as methane and the low digestibility of tropical forages. The objective of the study was to determine the effects of essential oils (EO) of Anacardium occidentale and Ricinus communis as additives in high forage diets on intake, digestibility, ruminal fermentation and synthesis of microbial protein. Four ‘Holstein’ steers fitted with ruminal cannula were used in a 4 × 4 Latin square design (21-day period). The treatments were 1, 2, 4 and 8 g day-1 EO per animal (essential oils, Oligobasics®). The diet was total mixed ration (TMR) of Brachiaria hay (Brachiaria humidicola cv. Lanero) and concentrate (ground corn, soybean meal, ammonium sulphate, urea and minerals) in an 80:20 ratio. Differences were observed in the digestibility of neutral detergent fibre (NDF) and total digestible nutrients (TDN) in levels above 2 g day -1 EO (P < 0.05). The VFA (volatile fatty acids) acetate and propionate were higher in diets with 2 g day -1 EO (P < 0.05), without affecting the acetate:propionate ratio. Levels above 2 g day -1 EO negatively affected the faecal N excretion (P < 0.05). The inclusions of A. occidentale and R. communis EOs at 2 g day-1 per day animal improved fibre digestion and decreased N excretion. These results indicate that this mixture of EOs may have strong antimicrobial activity at lower doses. The N losses, fibre digestion and digestibility could be improved with the use of cashew and castor essential oils in high forage diets.