Effects of supplementation of Bacillus subtilis natto Na and N1 strains on rumen development in dairy calves

Effects of Bacillus subtilis natto Na and N1 strains on ruminal development of papillae in dairy calves were investigated. Twenty four Holstein bull calves (7 ± 1.1 d) were randomly divided into three treatments of eight calves. The natto cultures Na and N1 were mixed with milk before weaning, or mixed with the concentrate portion of the diets after weaning. All calves were weaned when starter intake reach 20 g/kg of body weight. At weaning four calves were randomly selected from each group and slaughtered, and the remaining calves were fed the basal diet for additional 44 d and then slaughtered. Rumen fluid and ventral rumen tissue samples were collected from all calves. Results show that oral supplementation of B. subtilis natto Na or N1 reduced concentrations of short chain fatty acids in the rumen at weaning and 44 d after weaning (P<0.05). B. subtilis natto N1 reduced rumen pH and molar proportion of butyrate in both experimental periods (P<0.05), while B. subtilis natto Na decreased the molar proportion of acetate and ammonia levels at weaning (P<0.05) and depressed rumen NH3 concentration 44 d post weaning (P<0.05). The number and surface area of papillae per cm2 rumen wall for Na and N1 groups tended to be higher than the control at weaning (P<0.10) and 44 d after weaning (P<0.01). Furthermore, rumen papillae were flattened and tongue-shaped without narrow stalks, clumping or parakeratosis in the calves treated with natto culture. This study demonstrates that oral administration of B. subtilis natto Na and N1 increased rate of rumen development in dairy calves.