faecium 212 (PE; 1 × 109 + 1 × 109 CFU/d) on steers fed a 90% steam-rolled barley based diet. The probiotics did not affect ruminal pH, but P15 supplementation increased butyrate proportion and protozoa population with a concomitant reduction in amylolytic bacteria and S. bovis counts PRN1371 supplier [47]. In the other study, P. freudenreichii PF24 in association with Lb. acidophilus 747 (1 × 109 + 2 × 109 CFU/d) or Lb. acidophilus 747 and Lb. acidophilus 45 (1 × 109 + 2 × 109 + 5 × 108 CFU/d) given to mid-lactation Holstein dairy cows fed a 41% concentrate based diet did not affect the ruminal fermentations or pH, which was approximately 6.15 for control and probiotic-supplemented

cows [48]. According to our present hypothesis that probiotics become effective when the ruminal ecosystem is unstable, it appears that the conditions were not acidotic enough in the study of Raeth-Knight et al. [48], whereas the effects reported by Ghorbani et al. [47] may indicate a decrease in acidosis risk even though the ruminal

pH was not affected by probiotic supplementation [47]. In other studies reporting the use of probiotic bacteria, beneficial effects on ruminal pH were only observed for treatments associating bacteria and yeast [11, 12], and never for bacteria alone [29, 47–50]. Thus the beneficial effects on pH reported by Nocek et al. [11] and Chiquette [12] were probably not specific to the bacteria used, and may be attributed to S. cerevisiae, which has been

shown to stabilize ruminal pH [8, 9, 51]. However, a synergistic effect cannot be excluded as, to our knowledge, there have been no studies JAK inhibitor comparing yeast and bacteria Mannose-binding protein-associated serine protease used alone and in association. The present work is the first to report a specific positive effect of bacterial probiotics on ruminal pH during SARA. The mode of action of these probiotics, consisting of selleck inhibitor Lactobacillus and Propionibacterium selected strains, could not be clearly associated with quantitative characteristics of the rumen microbial ecosystem such as bacterial and protozoal populations. Conclusion This study shows for the first time that Lactobacillus and Propionibacterium probiotic strains may be effective in stabilizing ruminal pH and therefore preventing SARA risk, but they were not effective against lactic acidosis. The present results also suggest that the effectiveness of probiotics is compromised by ruminal fermentations, and are effective when the ruminal ecosystem is unstable. Although their mode of action needs to be further elucidated, we hypothesize that the effect of the probiotic strains used on ruminal pH was achieved by modulating the rumen microbiota, which was more diverse, by improving cellulolytic activity and by limiting the proliferation of lactic acid-producing bacteria. The combination of lactobacilli and Propionibacterium P63 seems to be more efficient in preventing SARA than P63 alone, possibly due to a synergistic effect between the strains.