Characterizing immunologic response to 5mg/kg and 8mg/kg IM SID dosing of Dexamethasone SP in Aspergillus infected broiler chickens.

Dexamethasone Sodium-Phosphate is a synthetic glucocorticoid used in a variety of species to treat inflammatory and autoimmune disorders. It has also been used as an immunosuppressive agent in studying disease common to immunosuppressed animals, such as fungal and respiratory infections and is currently in use to study vaccine efficacy in Aspergillus infected broiler chickens. There is limited research on the physiologic effects of Dex SP and appropriate immunosuppressive dosing protocols. It has been shown that Dex SP given at doses between 1-6mg/kg via IV, IM, and oral administration causes increased heterophil/lymphocyte ratio. The purpose of this study is to characterize the immunologic response to 5mg/kg and 8mg/kg IM Dex SP once daily for four days in chickens inoculated with A. fumigatus conidia to investigate the dosing regimen's effect on differential WBC counts and ability to respond to infection. Thirty-two SPF broiler chickens, divided into four groups, will receive a different combination of Dex SP and A. fumigatus conidia spores. Results of differential analysis by microscopic examination will be compared to standard differential reference ranges, providing insight to the degree of immunosuppression resulting from this specific dosing protocol. Further, any correlation between differential count and severity of infection will be investigated. The results will give indication as to the efficacy of this protocol in inducing immunosuppression. This will be useful in establishing guidelines on appropriate immunosuppressive dosing of Dex SP in chickens when used in vaccine studies, as well as useful information for veterinarians prescribing Dex SP in avian species.