Repeated ruminal dosing of Ruminococcus flavefaciens NJ along with a probiotic mixture in forage or concentrate-fed dairy cows: Effect on ruminal fermentation, cellulolytic populations and in sacco digestibility

Many studies have introduced exogenous bacterial strains into the rumen in an attempt to improve fermentation processes or counteract ruminal digestive disorders. Some attempts have been successful in the establishment of the new strain although others have failed. To a large extent, particular conditions necessary to the establishment of a new strain are not yet fully understood. In the present study, Ruminococcus flavefaciens NJ (NJ), isolated from the rumen of a wild moose, was introduced into the rumen of six ruminally fistulated non-lactating dairy cows receiving either a high concentrate or a high forage diet and supplemented on a daily basis with a probiotic mixture. In a second experiment, NJ and the probiotic mixture were given to young calves of 21 to 35 d of age. During repeated dosing, NJ modified the abundance of other cellulolytic bacterial populations compared with periods with no dosing. NJ also improved in sacco digestibility of timothy hay with the high concentrate diet. NJ declined rapidly in the rumen from 106 cells mL-1 after dosing to 102 cells mL-1, 24 h following dosing. The persistence of NJ increased with weeks of dosing in cows or when introduced in the rumen of young calves (105 cells mL-1 after 48 h and 102 cells mL-1 after 7 d). The presence of probiotics or a change in the concentrate to forage ratio in the diet did not succeed in establishing the new strain in the rumen. Key words: Ruminococcus flavefaciens NJ, probiotics, rumen fermentation, cellulolytic populations, in sacco digestibility, non-lactating dairy cows