The Effects Of Bacillus Subtilis Natto As DFM For Dairy Cattle

Bacillus subtilis natto has been authorized to be the microbiological feed additive. The research on the effects of bacillus subtilis natto as feed additive for dairy cattle is rare. In this study, three experiments, the purification and growth of bacillus subtilis natto, the effects of bacillus subtilis natto on rumen fermentation, and the effects of bacillus subtilis natto as feed additive for calves were investigated respectively. Strain No.4 was screened out with kinds of culture mediums and growth curves, and the conditions of its fermentation were optimized. The strain No.4 was identified as bacillus subtilis subsp subtilis by the physiological and biochemical ways according to Bergey's Manual of Determinative Bacteriology and the analysis on the 16sDNA sequence. The optimal growth conditions for the selected strain were 1% glucose, 1% sucrose, 6% soya peptone, 4% tryptone, 2% inoculation quantity and 5ml liquid medium in 100ml shake bottle. When the strain was fermented under the condition of 180r/min and 37℃for 24h, the OD at 660nm could reach 1.1475. The optimal growth condition selected was 180 r/min and 37℃. The multiplication results of liquid fermentation and solid fermentation were stable, and the quantities of bacteria were both 1010cFu/ml. The optimal culture time of solid fermentation was 36h. The results of artificial rumen experiments showed that 1% and 5% bacillus subtilis natto culture both increased the concentrations of volatile fat acids (VFA), indicating it could promote the rumen microorganism to digest and metabolize the carbohydrate. The bacillus subtilis natto culture affected pH, NH3-N, MCP and VFA in artifical remen. After adding bacillus subtilis natto culture, the pH in artificial rumen was significantly higher than that in control; 5% bacillus subtilis natto culture make the concentration of NH3-N higher than that in control; 1% bacillus subtilis natto culture made the concentration of NH3-N lower than that in control after culturing for 13h; after adding 1% and 5% bacillus subtilis natto culture, compared with that in control, the concentrations of the acetic acid, propionic acid, butyric acid, and total VFAs increased, indicating that it could promote the rumen microorganism to digest and metabolize the carbohydrate. Bacillus subtilis natto culture made the concentration of NH3-N increase and the value of MCP decrease, indicating that bacillus subtilis natto culture had interaction with the rumen microorganism community, the mechanism of the interactions between bacillus subtilis natto culture and different kinds of bacteria and protozoan needed further investigation. Fourteen Holstein male calves were divided into 2 groups randomly and fed with diet added bacillus subtilis natto culture until natural weaning. The effects of bacillus subtilis natto on the growth, performance and weaning age of sucking calves were investigated. The results showed the daily gain of experiment group was 26.5% higher than that of control before weaning (P<0.01); Daily intake of started diet decreased by 11.9%; Compared with the weaning age (57d) of the control, the weaning age (49.7d) of experimental group was brought forward (P<0.01). It could be concluded that bacillus subtilis natto as feed microorganism had wide application foreground.