Effects of the combination between selected phytochemicals and the carriers silica and Tween 80 on dry matter and neutral detergent fibre digestibility of common feeds

The overall objective of the current study was to evaluate the effects of 2 carriers (Silica, SIL, and Tween 80, T80) and their interaction with 8 phytochemicals (PCs), on in vitro dry matter and neutral detergent fibre digestibility (DMD, NDFD) of 3 substrates commonly used as feed for dairy cattle (soybean meal, maize meal and total mixed ration –TMR). A total of eight PCs were tested: 4 essential oils (EO) - cinnamon oil (CIN), clove oil (CLO), thyme oil (THY) and oregano oil (ORE) - and 4 essential oil active compounds (EOAC) - cinnamaldehyde (CIN-AC), eugenol (EUG), thymol (THY-AC) and carvacrol (CAR). A positive control with carrier and no PCs was tested for each substrate (CRR). Each PC was tested at 0.5 mg L−1 of medium on DMD and NDFD in an in vitro batch fermentation system. The incubation was performed twice at the intervals of 4 (DMD4, NDFD4) and 24 (DMD24, NDFD24) h. The PCs effect was significant on maize meal and soybean meal DMD24. The carrier’s effect was significant on soybean meal DMD24, indicating a depressive effect of T80 on soybean meal. The PC-carrier interactions were significant on both DMD and NDFD of the tested substrates, except for maize meal and soybean meal DMD24. The PCs-SIL combinations generally increased digestibility while the combination with T80 exerted positive effect only on maize DMD4. The PC-carrier combinations variably affect digestibility of different substrates and these interactions should be considered both for their scientific and commercial implications.HIGHLIGHTS PC-Carrier interactions affect in vitro digestibility. In general, the PC-SIL combinations increase digestibility while those with Tween 80 exert depressing effect. The PC-Carrier effect is variable depending on the degraded substrate.