Screening of forest tree leaves from North Eastern Himalayan region as feed additives for modulating in vitro rumen fermentation and methanogenesis from total mixed ration

Sustainable feeding practices using agroforestry plants with high nutritional value can replace costlier feed ingredients, reduce food feed competition and lower greenhouse gas emissions in ruminants. Therefore, the present study was conducted to assess nutritional value and in vitro rumen fermentation parameters of various unconventional tree leaves from North Eastern Himalayan region to widen phytobiotic feed additive sources for mitigating ruminal methanogenesis. Leaves of Chillowance (Schima wallichii), Khasre (Ficus hirta), Tree bean (Parkia roxburghii), Parari (Schefflera wallichiana), Simontonia (Exbucklandia populnea), Nevaro (Ficus auriculata), Da qing shu (Ficus hookeri), Sohiong (Prunus nepalensis) and Rubber tree (Ficus elastica) were collected and individually incubated with cattle rumen liquor to determine their effect on in vitro methanogenesis, microbial biomass production and dry matter digestibility. The range of OM, CP, EE, T-CHO, NDF, ADF and cellulose content in the tree leaves were 83.6-97, 8.6-30.8, 1.9-4.8, 70.5-84.7, 43-61, 17-43 and 9-26.4% on DM basis, respectively. Following 24 h incubation, it was observed that Schefflera wallichiana had highest dry matter digestibility (68.2%) followed by Prunus nepalensis (63.5%), while methane production was found to be lowest in Ficus hookeri (18.3 mL/g of digestible dry matter/24 h). Based on the results of in vitro fermentation studies, three promising tree leaves, i.e. Prunus nepalensis, Ficus hookeri and Schefflera wallichiana, were further screened for their use as additives by replacing 25, 50 and 100 mg of control substrate (40% concentrate mixture and 60% paddy straw). Methane production was significantly reduced up to 20.8% with the replacement of control substrate by Ficus hookeri leaves at graded levels. Furthermore, an average reduction of 13.3% was observed in case of methane production when Ficus hookeri was added as an additive in comparison to Schefflera wallichiana and Prunus nepalensis leaves. Microbial biomass production and dry matter digestibility were enhanced up to 17.9 and 3.4%, whereas methane production was lowered by 15.3% with the addition of above tree leaves as additives irrespective of levels. Therefore, it can be implied that leaves of Schefflera wallichiana, Prunus nepalensis and Ficus hookeri have the potential to act as rumen modifiers for improving rumen fermentation and reducing enteric methanogenesis in ruminants.