Resumo

Rumen microbes are responsible for fiber breakdown, leading to the production of volatile fatty acids (VFA) which constitute the major ruminants energy source. In addition, they provide the principal protein source for ruminants. Attempts to modulate fermentation in order to obtain better productive results have been traditionally applied, including the use of native probiotcs. Probiotics are live microorganisms that when administered confer benefits to the host. The objective of this work was to evaluate the effect of the administration of two native ruminal bacterial strains on VFA concentration patterns and ruminal pH. A probiotic administration trial was carried out with 15 cannulated male lambs. Animals were blocked by weight in 3 groups of 5 animals and were intraruminally inoculated every 48 h with approximately 10¹⁰ cells of tPseudobutyrivibrio ruminis 50C, Prevotella bryantii C5 or sterile culture media in control group. Diet was based on alfalfa hay, ad libitum, and crushed corn supplementation (1% of metabolic weight). After a 19-day adaptation period, ruminal content samples were taken from every animal at 8 AM (first meal intake) and every 2 h for 12 h, and then every 4 h until 24 h were covered. Samples pH was measured and VFA concentration (acetic, propionic and butyric) was determined by HPLC. The effect of strains addition was analyzed using a GLM procedure (SAS System) and significant differences were considered when p<0.05. Changes in VFA patterns and pH of ruminal contents were achieved with the administration of these strains. Animals treated with P. rumins 50C showed a higher production of butyric acid and acetic/propionic ratio. Treatment with P. bryantii C5 resulted in an increase of acetic and butyric acids concentration. Daily pH evolution was similar in every treatment but P. bryantii C5 group showed a slightly lower mean pH. Strains addition affected ruminal fermentation and particularly enhanced ruminal butyric acid production. This could be an interesting feature in a ruminal probiotic since this acid is related with higher milk production and has a higher energy yield than the other VFA. Further analysis involving physiological parameters and ruminal microbiota will complement these observations.