Effect of the addition of cellulolytic bacteria to ruminal bacteria on in vitro fermentation characteristics

Abstract

26 Background : Digestibility of fiber in the rumen is not due to enzymatic activity of individual 27 bacteria, but rather to their interaction, which complements their enzymatic functioning. Thus, 28 efficiency of fiber digestion depends on the diversity and density of cellulolytic bacteria. 29 Objective: To estimate in vitro production of biogas, methane, and fermentative characteristics of 30 cobra grass ( Brachiaria hibrido ) inoculated with ruminal bacteria (RB) in coculture with isolated 31 cellulolytic bacteria (ICB) from bovine (ICB bov ) or water buffalo (ICB buf ). Methods : ICB bov and 32 ICB buf were isolated from ruminal cellulolytic bacteria consortia using specific culture media for 33 cellulolytic bacteria. Both were morphologically characterized, and a Gram stain was performed. 34 In the in vitro gas production test, the substrate was cobra grass and the inocula were ruminal 35 bacteria (RB), ICB bov , ICB buf , Coculture bov (RB + ICB bov ) and Coculture buf (RB + ICB buf ). 36 Production of biogas and methane (CH 4 ), as well as dry matter degradation (DMD) and neutral 37 detergent fiber degradation (NDFD) were measured. A completely randomized design was used. 38 Results : ICB were Gram positive cocci. Accumulated biogas production at 72 h from ICB bov and 39 ICB buf was on average 42.11% of that produced by RB. The Coculture bov produced 14.24% more 40 biogas than RB. CH 4 production was lower in ICB bov and ICB buf than in RB, Coculture bov and 41 Coculture buf . DMD and NDFD were not different among RB, Coculture bov and Coculture buf . ICB bov 42 degraded 37.10 and 96.34% more DMD and NDFD than ICB buf (p<0.05). Conclusion : The use of 43 ICB from bovine or water buffalo in coculture with RB does not improve in vitro production of 44 biogas, DMD or NDFD with respect to RB alone.