Ruminal Methane Emissions In Vitro of Plants Differing in Their Main Phenolic Fractions

Abstract

Plants containing phenolics have been known to produce less ruminal methane emissions when incubated with buffered-rumen fluid in vitro. However, little is known concerning methane mitigation effects of plants differing in their phenolic fractions. The present study was aimed to observe such effects by using several plants, namely Swietenia mahagoni (SM; rich in condensed tannins), Clidemia hirta (CH; rich in hydrolysable tannins) and Eugenia aquea (EA; rich in non-tannin phenolics). The plants were incubated either individually or mixed with a control plant with negligible phenolic contents, i.e. Carica papaya (CP; 1:1 w/w). An amount of 200 mg dry matter from each plant sample was incubated in vitro with 10 ml of rumen fluid and 20 ml of buffer solution in a Hohenheim gas test syringe. Incubations were conducted in four replicates (runs), represented by one syringe per replicate. In each run, incubation was performed for 24 h and kept at 39oC. Total gas and methane productions were measured after the incubation. Fermentation fluid was subjected to volatile fatty acid (VFA) and ammonia measurements as well as bacteria and protozoa counts. Data were analyzed by analysis of variance and subsequent Duncan’s test. Results revealed that combining each species of plant containing phenolics with CP significantly lowered methane emissions (as percentage of total gas) (P<0.05). Methane emissions of CP, CP+SM, CP+CH and CP+EA were 18.6, 14.0, 14.3 and 16.1%, respectively. Total gas production of CP decreased significantly after being mixed with SM, CH and EA (P<0.05). Similar pattern to total gas was observed for those of total VFA and ammonia concentrations. It can be concluded that methane mitigation effects of plants rich in either condensed or hydrolysable tannins are higher than that of plant rich in non-tannin phenolics.