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Coccidiosis in commercial broiler chickens: Improving management of Eimeria species using live-vaccination or anticoccidial medication and developing and applying quantitative species-specific molecular assays.

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Title: Coccidiosis in commercial broiler chickens: Improving management of Eimeria species using live-vaccination or anticoccidial medication and developing and applying quantitative species-specific molecular assays.
Author: Snyder, Ryan
Department: Department of Pathobiology
Program: Pathobiology
Advisor: Barta, John
Abstract: Eimeria species are the cause of intestinal disease coccidiosis and impose a burden to commercial broiler production. The two most widely used coccidiosis prevention strategies include in-feed medication or live-vaccination. Commercial broiler flocks (n=95) in Ontario were sampled to determine oocyst cycling patterns to measure the success of medicated or vaccinated prevention programs at controlling disease. Vaccinated flocks (n=42) had more consistent oocyst shedding patterns with earlier and lower maximal counts than medicated flocks (n=53). Samples collected in the summer months peaked earlier in broiler production than winter months regardless of prevention program. Vaccinated flocks were on an antibiotic free program and at least some flocks suffered from bacterial necrotic enteritis, thereby reducing production efficiencies. One facility was identified with apparent anticoccidial-resistant Eimeria. This facility was seeded with sensitive Eimeria strains by vaccinating two consecutive flocks. Based on two Anticoccidial Sensitivity tests performed on isolates from before and after the seeding, the drug sensitivity profile improved. Oocyst cycling in flocks after seeding had shown improvement. However, neither the robustness nor longevity of this improvement could be assured because of the legislative requirements for Canadian broiler producer to remove litter at the end of flocks, thereby decreasing the carryover of drug-sensitive Eimeria population. The identification of the multiple Eimeria species typically found in a sample becomes essential because of their unique pathological characteristics and commercial impacts. Molecular assays were developed and tested provide relative species abundance. High throughput amplicon sequencing using Next Generation Sequencing and target quantification using Droplet Digital PCR both proved to be reliable diagnostic assays when targeting the cytochrome c oxidase subunit III gene within the mitochondrial genome. Finally, the ingestion rate of topically applied coccidiosis vaccines directly impacts the initiation of oocyst cycling required for broiler flocks to become protected from Eimeria challenge. Microspheres and fluorescein were used as tracers to measure the volume of material ingested by chicks following vaccination with either coarse spray or gel droplet applications. Together, this work explores the current strategies to prevent coccidiosis, methods to improve the effectiveness of these strategies, and applies new technologies to the diagnostics of Eimeria species infections.
URI: https://hdl.handle.net/10214/23704
Date: 2021-01
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