Abstract: Two types of Bacillus subtilis natto culture (Na,N1) were added to the milk/starter/feed to evaluate effects on the fermentation of rumen and the enzyme activity. 24 Holstein bull calves of (7±1) d of age were divided into three treatments: Calves in treatment 1 were fed with the N1 type of Bacillus subtilis natto culture; treatment 2 with Na type of Bacillus subtilis natto culture, control group with none of those two types of culture. The calves were fed with milk supplemented with the Bacillus subtilis Natto, and starter diet was also fed to the calves until weaning. Calves were weaned until their intake of starter was up to 2% of their weight, and four calves were slaughtered randomly after weaning. Other calves were fed with the basal diet with or without Bacillus subtilis natto cultures as before and the calves were slaughtered eight weeks after weaning. The results were as follows:① compared with the control and treatment 2, the pH values in the rumen of the calves in treatment 1 were significantly lower (P<0.05).② The concentration of VFA in the rumen of calves in treatment 1 and 2 was remarkably lower than the control group. No difference was observed in the molar percentage of acetic acid among the three groups after weaning, but eight weeks later, the molar percentage of acetate acid was significantly lower in the N1 group than that in the control (P<0.05).On the contrary, there was remarkable difference in the molar proportions of propionic acid at the time of weaning compared to the control(P<0.05), but no differences existed among the three groups eight weeks after weaning.③ At the time of weaning, the mean NH3-N concentrations in treatment 1 and 2 were lower and significantly lower than that in the control group, respectively. Furthermore, the mean NH3-N concentrations in the two supplemented treatments were dramatically lower than the control eight weeks after weaning(P<0.05).④The activity of protease was higher in the control group than in the other two treatments throughout the whole experiment (P<0.05),however，that of exoglucanase was significantly lower(P<0.05),although no difference was observed on the activity of endoglucanase and β-glucosidase among those three groups. The experiment instructed that the effects of different types of Bacillus subtilis Natto on cows at different stages verified. Supplementation of Bacillus subtilis Natto was beneficial for the development of rumen in calves, which promote the growth of the calves.

Key words: Bacillus subtilis Natto; calves; volatile fatty acid; rumen fermentation; enzyme activity