Abstract: Evaluation of the development of resistance following prolonged use of synthetic anticoccidials in a high challenge floor pen model
Prolonged use of a single chemical coccidiostat has been associated with the development of resistance in coccidia strains. However, the nature and timeline of resistance development has not been well characterized for all anticoccidials. A previous series of studies using an undefined challenge indicated a gradual decrease in efficacy over time among tested treatments.
The purpose of this series of studies was to assess the development of resistance to four synthetic anticoccidials when used over four successive broiler grow-out cycles. Additionally, two of the anticoccidials were used at higher inclusion levels to increase the likelihood of resistance development.
In contrast to the previous study series, a challenge inoculum was collected and used to supplement the natural challenge in the litter during each study. Resistance development was assessed based on feed conversion ratios, average body weights and mortality by feeding phase. Coccidiosis lesions were evaluated at 16, 22 and 26 days.
The results of this series are pending.
This study was conducted by Nicholas Brown Huvepharma, Inc. It was presented at the 2025 American Association of Avian Pathologists annual meeting.
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