The impact of helminth infections in free-range chickens with special focus on the pathologenicity of tetrameres americana
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Date
2003
Authors
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Publisher
Sokoine University of Agriculture
Abstract
The distribution of helminth infections in free-range chickens is known to be wide
spread and some of the species occur with high prevalence and intensities, but the impact of helminth infections has not been adequately quantified. Two on-farm studies were conducted: the first was to determine the effect of natural helminth infections and the second was to evaluate different treatment regimens in free-range chickens. In addition two on-station experimental infections ol’ Teiranicrex americana were conducted to determine the pathogenic effect of this parasite. Twelve farms were involved in the on-farm studies where anthelmintics were applied strategically, in the first experiment a single dose of mebendazole was applied fortnightly and the chickens were followed for six months. In the second experiment the chickens were followed for 12 months where single, seasonal, and month!} treatments were tested. Mortality. weight, and egg production were recorded e\cr\ fortnight for the entire experimental period. lor the on-station studies the pathogenic effect ol dillcrcnt mlcciivc doses ol /.
iimeriuanci were assessed for 12 weeks. The parameters measured were: mortality. weight gain, and the effect on haematological profiles. The results of the on-farm studies showed that natural helminth infections in free-range chickens reduced growth rates by 22% and delayed sexual maturity by eight weeks. The following helminth species were noted to cause mortalil}: Axcuridiu tiulli (one deal!'.) and Xy/i^uiiuis truchcu (15 deaths) and Helerukis i’uUinurum (17 deaths) through transmission of histomonosis. Monthly treatment was a better regimen but seasonal treatment was very promising. In the experimental infection 7! timcricaim produced transient anaemia: lymphocytopenia.: 11 heterophilin. eosinophilia, and elevated blood pepsinogen levels. The key findings from the present studies are that natural mixed helminth infections cause a subclmicai disease resulting in slow grow ill rale and dclascd sexual maturilj in ri ce-range chicken. 1’or the first time T. cuneiiccinci has been observed to elevate the blood pepsinogen level as well as causing low weight gains and that a mean ol’X 7 female /’ uiiicricciiiu intermittent!)
caused anaemia.
Description
PhD Thesis
Keywords
Helminth infections, Pathologenicity, Free-range chickens, Tetrameres Americana