Effects of carvacrol and cinnamaldehyde on microbial fermentation when added to a barley- or corn-based diet in a continuous-culture system

Six dual-flow continuous-culture fermenters (1300 mL) were used to evaluate in a 2 × 3 factorial arrangement the effects of carvacrol (CAR) and cinnamaldehyde (CIN) supplementation [0.2 g kg-1 of dietary dry matter (DM)] and the source of grain (barley vs. corn) on microbial fermentation. Inoculum was collected from four ruminally cannulated lactating Holstein cows fed a mixed diet of 50% forage and 50% concentrate (16.3% crude protein, 33.5% neutral detergent fiber, DM basis). The experimental period consisted of 10 d, with the first 6 d for adaptation to experimental treatments, and 4 d of sample collection. Fermenter pH was lower for corn- than for barley-based diets (6.14 vs. 6.27; P < 0.05). True crude protein (CP) degradation tended (P = 0.10) to be higher for barley- than for corn-based diets (47.0 vs. 41.3%). Neither CAR nor CIN altered fermentation parameters [pH, NH3-N, total volatile fatty acid (VFA) concentration, and molar proportions of individual VFA], nutrient digestibility, N metabolism, and efficiency of microbial protein synthesis. The results of this study show that at the dosage selected (0.2 g kg-1 of dietary DM), CAR and CIN had no effects on microbial fermentation, feed digestibility, and N metabolism in continuous-culture fermenters fed a barley- or corn-based diet. Key words: Essential oil compound, barley, corn, continuous-culture system