In vitro ruminal dry matter and neutral detergent fibre digestibility of common feedstuffs as affected by the addition of essential oils and their active compounds

The effects of essential oils (EO) and their active compounds (EOC) on dry matter digestibility and neutral detergent fibre digestibility (DMD and NDFD, respectively) are still not enough described since in vitro methods are limited. So, the aim of the study was to screen and compare the main effects of EO and EOC on short-term DMD and NDFD using the in vitro method. The addition of phenylpropanoid-rich cinnamon oil (CIN) and clove oil (CLO), terpenoid-rich thyme oil (THY) and oregano oil (ORG), and four EOC: cinnamaldehyde (CIN-C), eugenol (EUG), thymol (THY-C) and carvacrol (CAR) was studied at a dose of 0.5 mg · l−1 of main active compound. Products were tested on four substrates: lucerne hay, soyabean meal, maize meal and a total mixed ration (TMR). Digestibility was determined at 4 and 24 h of fermentation. Both CIN and CIN-C increased NDFD4 of lucerne and maize meal, and decreased NDFD24 of soyabean meal; while CIN-C reduced NDF24 of TMR and CIN reduced DMD of soyabean at both examined hours. CLO and EUG decreased the NDFD24 of soyabean meal improving its DMD24. Also initial DMD of lucerne was increased by both these factors. Only CLO reduced NDFD24 of maize meal. Both THY and THY-C reduced DMD4 of soyabean meal; however only THY-C improved NDF4 of lucerne and reduced NDFD24 of soyabean meal and TMR. DMD24 of most substrates (except lucerne) was reduced by ORE, but not by CAR which improved NDFD4 of lucerne. The in vitro method was sensitive to variations in digestibility caused by EO and EOC, providing a promising approach for the incorporation of EO and EOC effects in systems for cattle diet formulation