| The present study investigates the impact of Bacillus subtilis with diverse bacteriostatic properties on the intestinal health and growth performance of broiler chickens.The experiment employed ETEC K88 infection as the test model and conducted in vitro bacteriostatic assays to validate the efficacy of Bacillus subtilis in broiler chickens.The preliminary findings are summarized below:1.Initially,a variety of Bacillus strains were isolated from soil and broiler feces of broiler farms based on their colony morphology.After isolation and purification,physiological and biochemical indices of Bacillus,16S r RNA gene sequencing,and preliminary bacteriostatic evaluations were conducted.Three Bacillus subtilis strains with distinct bacteriostatic properties(designated as Bacillus subtilis B,D,and G)were identified and screened.Subsequently,the growth curves,tolerance,enzyme production performance,and bacteriostatic properties of these strains were investigated.The Oxford cup method was employed to assess the antibacterial efficacy of the three Bacillus subtilis strains,and the results indicated that strain D displayed superior antibacterial activity against Escherichia coli and low sensitivity to lactobacilli,hence demonstrating better overall bacteriostatic performance compared to strains B and G.2.In the animal experiment,200 1-day-old AA broiler chickens were selected and divided into 5 treatment groups according to the principle of initial weight consistency.The five treatment groups were as follows:1)NCH group with oral normal saline and feeding basal diet;2)CH group oral ETEC K88,feeding basic food group;3)CH-G group oral ETEC K88,feeding Bacillus subtilis G group;4)CH-B group oral ETEC K88,feeding Bacillus subtilis B group;5)CH-D group oral ETEC K88,feeding Bacillus subtilis D group.In the broiler group for 7 days,the NCH group was tested with 1 m L of normal saline in broiler chickens orally and the other 4 groups were treated orally with 1 m L of ETEC K88 bacterial solution(1.0×10~8 cfu/m L).The dosages of Bacillus subtilis B,D and G preparations for the test were 1.0×10~7 cfu/g full compound feed.On day 21 of the test,growth performance data statistics;at the same time,intestinal p H was determined,broiler small intestine and cecum and chyme samples were taken,and intestinal flora,intestinal morphology,and jejunal digestive enzymes were determined.The test results showed:(1)Relative to their NCH counterparts,broiler chickens in the CH group exhibited a significant decline in minced weight,average daily weight gain,and average daily feed intake(P<0.05),with a simultaneous increase in the feeder-to-weight ratio and diarrhea index(P<0.05).Contrarily,compared to CH broilers,ground weight and average daily gain of CH-D broilers increased significantly(P<0.05),while the feed-to-weight ratio and diarrhea index demonstrated a substantial decrease(P<0.05).(2)Relative to their NCH counterparts,the p H values of both jejunum and rectum of CH broiler chickens registered a substantial reduction(P<0.05),while no significant difference in p H values of duodenum,ileum,and cecum were observed(P>0.05).Similarly,there were no significant differences in the p H values of all digestive tracts such as jejunum,ileum,cecum,and rectum of CH-G,CH-B,and CH-D broilers as compared to the CH group(P>0.05).(3)In contrast to NCH broilers,CH broiler chickens exhibited a significant decline in total amylase enzyme activity in jejunal chyme(P<0.05),while no significant effect was observed on total protease enzyme activity(P>0.05).On the other hand,compared to the CH group,the CH-D group showed a noteworthy elevation in total chyloamylase in broiler jejunal chyme(P<0.05),but no significant effects were found on total chyle amylase and total protease in broiler chickens in the CH-G and CH-B groups(P>0.05).(4)Compared with NCH broiler chickens,CH broiler chickens exhibited a significant increase in the number of chyme E.coli in both small intestine and cecum,and a decrease in the number of lactobacilli and lactobacillus/E.coli ratio(P<0.05).Among the treatment groups,CH-B and CH-D broilers demonstrated a significant decrease in the number of small intestine and cecal E.coli bacteria,while CH-D broilers showed a significant increase in the number of small intestine and cecal lactobacillus and lactobacillus/E.coli ratio(P<0.05).No significant differences in the intestinal flora of CH-G broilers were observed when compared with CH broilers(P>0.05).(5)Compared to NCH broilers,CH broilers exhibited a significant reduction in the ratio of jejunum and ileal villi height,as well as villi height/crypt depth(P<0.05),while crypt depth was significantly increased(P<0.05).Conversely,the aforementioned ratios were significantly increased(P<0.05)and crypt depth was significantly decreased(P<0.05)in CH-D broilers when compared to CH broilers.However,no significant differences were observed between CH,CH-G,and CH-B broiler groups with respect to the aforementioned ratios(P>0.05).In summary,the in vitro antibacterial activity and feeding efficacy of strain D were superior to those of strains B and G.These results demonstrate significant variations in the bacteriostatic performance of different Bacillus subtilis strains,and suggest that comprehensive in vitro bacteriostatic experiments can efficiently identify high-quality Bacillus subtilis preparations.Such preparations can enhance the growth performance of broiler chickens infected with ETEC K88 by regulating the intestinal flora and preserving the intestinal morphology. |
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