Effect of Antibiotics on the Growth Performance, Intestinal Immunophysiology and Gut Floral Composition in Broilers
Date Issued
2008
Date
2008
Author(s)
Hung, Ching-Chi
Abstract
The use of antibiotics as a growth promoter will be eliminated in the near future. In order to assess the impact of antibiotic substitutes on intestinal fuctions, the basic and antibiotic-induced changes on growth, intestinal immunophysiology and gut flora composition were investigated in broiler chickens. One hundard ninety two broilers were randomly allocated to 4 treatments with 4 replicates of 12 birds eachfor treatment. The 4 treatments were: control, 20 ppm colistin, 55 ppm tylosin and 55 ppm chlortetracycline supplementation. The intestinal physiology, gut flora composition in the intestine and immune function were measured at 0, 3 and 6 weeks of age. Results showed that the body weight gain and feed efficiency were significantly increased in colistin and tylosin supplementation group, but were not in chlortetracycline group at 6 weeks of age when compared with control (P<0.05). The short-circuit current and conductance of ileum in colistin group were greater than control (P<0.05). Gut mucosal maltase and sucrase activities were increased (P<0.05) in the colistin and tylosin groups at 6 weeks of age. In intestinal morphology, the colistin supplemented group had increased villus area in jejunum and ileum. The tylosin group showed decreased musculars mucosal thickness and crypt depth in jejunum but not in ileum (P<0.05). However, the addition of chlortetracycline increased the thickness of muscular mucosa in jejunum and ileum compared with control (P<0.05). In the aspect of gut flora composition, the coliform counts were also decreased in the intestine of colistin and tylosin supplementation groups at 6 weeks of age, but no significant difference was seen in chlortetracycline when compared to control. Enteric bacteria were present in liver of control chickens during experimental period. All antibiotics supplementation significantly inhibited the phemomena of bacteria translocated to the liver and spleen at 3 weeks of age. For immune responses, there were no significant difference in splenocytes proliferation and myeloperoxidase activity among treatments. In the aspect of humoral immune fuction, the antibiotic groups all displayed increased IgG antibody in blood when compared with control group (P<0.05). The tylosin supplemented group had increased antibody titer against Infectious bronchitis at 3 weeks of age and enhanced expression of T cell receptor γδ at 6 weeks of age, but decreased blood IgA levels and secretory IgA in the mucosa of jejunum (P<0.05). The chlortetracycline supplementation improved intestinal innate immunity by increased mucosal antimicrobial lysozyme level (P<0.05). In conclusion, the growth enhancement and increased feed intake by colistin and tylosin antibiotic supplementations were possibly due to reduce numbers of gut pathogenic bacteria and less translocation to intestinal organs, increase gut disaccharidase activities and augmentation of IgG antibody levels.
Subjects
Antibiotics
Intestinal physiology
Immunity
Type
thesis
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