Experimental animals and dietary preparation Just after slaughter the fresh rumen contents were collected into polyethylene bag and carried out to the Animal Nutrition Field Laboratory, Faculty of Veterinary and Animal Science, Sylhet Agricultural University, Sylhet. Processing methods was followed According to application of heat, sun-drying, oven drying (Tukur et al., 2001; Adeniyi and Balogun, 2002). It was allowed initially for sundry and stored for feeding the animal as the substitute of goat feed. At the eve of feeding the dried digesta was sterilized at 121°C using autoclave.
The animals were fed two times a day. At the morning and evening, every groups (T0, T1) were allowed to feed almost similar fresh roughage (4kg fresh napier grass) but incase of concentrate feeding, the control group (T0) was not allowed to feed the rumen ingesta and molasses. Meanwhile, the treated group (T1) was allowed to feed 92g dry matter (DM) rumen ingesta (sterilized at 121°C) and 12.5g (DM) molasses. In case of mixed concentrate feeding, the control (T0) animals were supplied 315g (DM) feed comprising with maize, wheat bran, soyabean meal, gram, khasari bran and some vitamin mineral premix at morning and evening. On the other hand, for T1 mixed concentrate of T0 with rumen ingesta and molasses were supplied twice a day.
Sample collection, preparation and chemical analysis At the eve of the experimental period, the fresh rumen ingesta, concentrate feed ingredients were collected, sundried, grinded and sterilized. The representative samples were chemically analyzed at the Department of Animal Nutrition, Faculty of Veterinary and Animal Science, Sylhet Agricultural University, Sylhet analytical laboratory.
Bio-gas production and methane estimation Fresh rumen injesta was collected into the beaker just after slaughtering the animals from the government slaughter house of Sylhet City Corporation at the early of morning. The glass beakers were tried to maintain at anaerobic condition by wrapping the mouth with rubber gloves. Then the beakers were carried out to the Animal Nutrition Laboratory within a temperature-controlled sample/tool box. The content of beakers were measured using electric balance and close observation was maintained to collect the stored emitted gas into the syringe from the fermented content gradually at 0, 1, 2, 4, 6, 8, 12,16, 24, 36, 48, 72 and 96 hours intervals. The gross gas was react with Ca(OH)2 to determine the CO2 level and finally the CH4 level.
Statistical analysis The experiment was arranged at completely randomized block design and the data were analyzed using SAS 9.1.1 computer program. The analysis of Co-variance (ANOVA) was determined and Duncan's Multiple Range Test (DMRT) was done to differentiate the variables.