Abstract: This experiment was conducted to study the effect of Bacillus subtilis on growth performance and immunity in broilers. 200 one-day AA bilers with similar body weight were randomly divided into 5 groups with 4 replicates in each group, and with 10 broilers in each replicate.The groups received the same basal diet supplemented with 0, 2×10⁵,5×10⁵,8×10⁵ and 1×10⁶ CFU/g of Bacillus subtilis, respectively. The feeding trial lasted 42 days. The results showed as follows: in every test period, compared with the control group, the average daily gain in the group Ⅱ was higher, the F/G in group Ⅱ was lower, except at the age of 29 to 35 days. At the age of 36 to 42 days, the average daily gain in group Ⅱ increased significantly by 10.25%(P<0.05), the F/G in group Ⅱ decreased significantly by 14.83%(P<0.05), at the age of 28 days, the spleen index was significant higher than those in the control group, higher above 31.96% (P<0.05),the bursa of fabricius index in group Ⅱ was significant higher than those in the control group, except at the age of 14 and 28 days, the antibody titer in group Ⅱ was higher than those in the control group, at the age of 28 and 35 days, higher above 16.04% and 18.09%, respectively(P<0.05);at the age of 21,35 and 42 days, the serum immunoglobulin G concentrations in group Ⅱ was higher those in control group, higher above 81.94%, 46.67% and 15.63%,respectively(P<0.05). In conclusion, adding 5×10⁵ CFU/g Bacillus subtilis B7 in diet could improve the growth performance and enhance the immune function of broilers. These results indicated that the 5×10⁵ CFU/g was the best supplementation.

Key words: Bacillus subtilis; broilers; growth performance; immune function