Resumo

Rumen microbiota is responsible for fiber breakdown and volatile fatty acids (VFA) produced provide the major energy source for ruminants. The resultant microbial biomass is used by ruminants as the principal protein source. Attempts to modulate fermentation in order to obtain better productive results have traditionally been applied, being the use of native probiotcs a possible alternative. Probiotics are live microorganisms that when administered confer benefits to the host. The objective of this work was to evaluate the effect of different ruminal bovine bacterial strains on in vitro gas production kinetics, VFA patterns and methane production. Two Pseudobutyrivibrio ruminis, 3 Butyrivibrio hungatei and 2 non-described members of the Familiy Lachnospiraceae were used in an in vitro model performed in batch cultures with milled Lucerne hay and corn (70:30) as substrate. Gas volume was calculated from pressure data and accumulated gas along time was adjusted according a mathematical model to obtain fermentation kinetics parameters. At 4, 8 and 96 h, pH was measured and VFA (acetic, butyric and propionic acids) concentration was quantified by HPLC. Also, methane concentration was determined by GC. The strains addition effect was analyzed applying a GLM procedure (SAS System) and comparing with the control that had no strain added, significant differences were considered when p<0.05 Strains addition modulated fermentation in different ways. Total gas volume was not affected but 4 bacterial strains enhanced the volume and the rate of gas production of the slow phase of fermentation, associated to fiber degradation. VFA patterns were also affected. Particularly, strains addition significantly affected acetic-propionic ratio and at time point 8 h one strain significantly enhanced butyric acid concentration. Four treatments showed higher pH values than the control and no differences in methane concentration were found. Strains addition affected in vitro fermentation by changing gas production kinetics and VFA patterns but methane concentration was not affected. Strains that enhanced insoluble fiber degradation kinetics are promising candidates to be used in in vivo approaches. Future analysis of the flask’s microbial community will shed light to the understanding of the observed fermentation changes.