Assessment of the effects of cinnamon leaf oil on rumen microbial fermentation using two continuous culture systems

Two continuous culture (CC) systems, the Rumen Simulation Technique (RUSITEC) and a dual-flow (DF) fermenter, were used to evaluate effects of the essential oil from cinnamon leaf ( CIN) on rumen microbial fermentation. Incubations (d 1--8 for adaptation and d 9--16 for sampling) were conducted concurrently in the two systems, with CIN added at 0 (control) and 500 mg/L of rumen fluid culture. Eight RUSITEC (920 mL; dilution rate = 2.9%/h) and six DF (1300 mL; dilution rate = 6.3%/h) fermenters were randomly assigned to treatment. Inoculum was prepared from four ruminally cannulated lactating Holstein cows fed a TMR consisting of 46.5% of forage and 53.5% of concentrate (DM basis). Ruminal pH, total volatile fatty acid (VFA) concentration, and diet digestibility were reduced by CIN addition in the RUSITEC but were not affected by CIN administration in the DF. The addition of CIN in the RUSITEC decreased apparent N disappearance, NH3-N concentration, and molar proportions of branched-chain VFA (BCVFA). In contrast, in the DF, no effect of CIN was observed on apparent N degradation, NH3-N concentration, and molar proportion of BCVFA. In the RUSITEC, the molar proportion of acetate was similar between treatments on d 9 and d 13, but was lower from d 10--12 and higher on d 14--16 with CIN than with control (interaction treatment x sampling day). The molar proportion of acetate remained unaffected by CIN addition in the DF. In both CC systems, propionate molar proportion was decreased while that of butyrate was increased by CIN addition. In the DF, CIN decreased microbial N flow and efficiency of microbial protein synthesis. Protozoa numbers were lower with CIN than with control in both CC fermenters. In the RUSITEC, CIN increased 15N enrichment in total bacterial fractions, but no effect was observed on the production of microbial nitrogen. This study showed that CIN exhibited antimicrobial activity in both CC systems, but the effects were more pronounced with the RUSITEC than with the DF. These differences are likely a reflection of the higher dilution rate in the DF resulting in a lower effective concentration of CIN in DF than in RUSITEC. Based on these changes in rumen microbial fermentation, supplementation of CIN at the concentration evaluated in this study may not be nutritionally beneficial to ruminants.