AimsThis study was carried out to determine the effect of graded levels of tannin-containing tropical tree leaves, Autocarpus integrifolis, Azardirachta indica and Ficus bengalensis, on the in vitro rumen fermentation pattern, total protozoa and methane suppression in order to establish the optimum dose of these leaves for inclusion in the ruminant diets. Methods and ResultsThe air-dried and ground samples of Au.integrifolis, Az.indica and Ficus bengalensis were subjected to in vitro incubation using 30ml buffered rumen fluid at 0, 25, 50, 100, 150, 200, 250 and 300% (dry matter refers to moisture-free basis) of a total mixed ration (TMR: refers to mixture of roughage and concentrate containing cereals and oil cakes) devoid of tannin. The TMR for the experimental incubation was prepared by mixing 40 parts of ground Elusine coracana straw as roughage source with 60 parts of concentrate mixture. The leaves contained an average 130gkg(-1) CP with 70MJ of MEkg(-1) DM. The average neutral detergent fibre (NDF) content was <400gkg(-1) DM. Highest total phenol (TP; gkg(-1)DM) was recorded in Az.indica (108) followed by F.bengalensis (103) and Au.integrifolis (76), and total tannin (TT) content also showed similar trend. However, condensed tannin (CT) was highest in F.bengalensis (260) followed by Au.integrifolis (186) and Az.indica (138). There was significant (P<005) reduction in the NH3 concentration in the presence of all the leaves. Autocarpus integrifolis tannins did not cause inhibition of total volatile fatty acid (TVFA: refers to the concentration of volatile fatty acids, viz. acetic, butyric and propionic) concentration, whereas F.bengalensis and Az.indica tannins at higher level of incubation (>50%) reduced TVFA concentration. Protozoa (cells per mL) were similar at all levels of inclusion with Au.integrifolis, but reduced in case of F.bengalensis and Az.indica. As the level of tannin increased in the incubation medium, there was a linear reduction in methane concentration. Highest methane reduction (%) was recorded in incubations supplemented with Az.indica (615) followed by F.bengalensis (468) and Au.integrifolis (303). ConclusionsIt was established from this study that tropical leaves of F.bengalensis, Au.integrifolis and Az.indica suppress methanogenesis. Significance and Impact of the StudyFicus bengalensis, Au.integrifolis and Az.indica leaves are of interest in the enteric methane ameliorative strategies. Total mixed ration containing 10-15% ground F.bengalensis or Au.integrifolis or Az.indica leaves could be fed to ruminants to reduce enteric methanogenesis. However, in vivo trials need to be carried out to validate these in vitro results.