BIOGAS PRODUCTION AND FERMENTATION CHARACTERISTICS in vitro OF CELLULOLYTIC RUMINAL BACTERIAL CONSORTIUMS OBTAINED FROM DIFFERENT FIBERS

Background. Cellulolytic bacterial consortia (CBC) serve as additives to improve fiber degradation in ruminants, since they improve biogas production and in vitro fermentation characteristics. Objective. To evaluate the biogas production and fermentative characteristics in vitro of mulato grass inoculated with ruminal CBC obtained from ground sawdust, ground mulato grass or whole stem as substrates in the selective culture medium. Methodology. The CBC were obtained from ruminal fluid from a Suiz-Bu cow fitted with a ruminal cannula, which was transferred six times in a selective anaerobic medium. The test consisted of preparing sterile biodigesters with 0.5 g of mulatto grass with 63 d of regrowth, 45 mL of culture medium. The inoculation was with 5 mL of a type of CBC. The biodigesters were incubated 72 h at 39 °C. Biogas production was measured at 3, 6, 9, 12, 24, 48 and 72 h. In the culture media, ammonia nitrogen (N-NH3), total bacterial count, cellulase activity, pH, dry matter degradation (DMD) and neutral detergent fiber degradation (NDFD) were determined at 12, 24, 48 y 72 h. In the biogas production a completely random design was used; while in the rest of the variables a completely randomized design was carried out with a 3x4 factorial arrangement, with fiber source and incubation time as factors. Results. The biogas production of the CBC obtained from the ground grass showed higher (p<0.05) accumulated production in all the evaluated times. The CBC obtained from sawdust increased the biogas production by 175% from 24 to 48 h and by 313% from 48 to 72 h. There was an interaction effect (p <0.05) on DMD, NDFD, N-NH3, total bacterial count and cellulase enzymatic activity. The CBC obtained from ground mulatto grass at 72 h increased (p <0.05) the DMD and NDFD. The CBC obtained from sawdust increased DMD by 19.1% and NDFD by 33% from 48 to 72 h. The concentration of bacteria in the observed interactions is within the range of the ruminal ecosystem. The highest (p<0.05) content of N-NH3 was determined when the CBC obtained from grass stem with 12, 24 and 72 h of incubation were used. Implications. Using the same fiber source to obtain the CBCs improves the degradation of said fiber. Conclusion. The size and source of fiber are decisive in the type of bacteria that make up the cellulolytic bacterial consortia of ruminal origin under the conditions of this in vitro test.