Parasitic Reinfection in Wild Northern Bobwhite (Colinus virginianus) Following Consistent Treatment with a Biannually Administered Anthelmintic Feed

Northern bobwhite (Colinus virginianus) populations have experienced sustained declines across their native range, with parasitic helminths, particularly the eyeworm (Oxyspirura petrowi) and cecal worm (Aulonocephalus pennula), emerging as contributing stressors. This study assessed the long-term efficacy of a biannually administered anthelmintic feed treatment (QuailGuard®) and characterized seasonal and annual reinfection patterns in wild bobwhite populations at 2 sites (Oklahoma and Texas) from 2023 to 2025. Fecal samples were collected from wild bobwhite from March to October and analyzed via quantitative polymerase chain reaction (qPCR) to estimate infection levels. Aulonocephalus pennula infection levels were consistently reduced following spring and fall treatments, with efficacy ranging from 61 to 92%, except for 1 unsuccessful treatment in the fall of 2024 at the Texas site. Reinfection was rapid during the summer, and overwinter reinfection was more severe in 2024-2025 than the previous year. Oxyspirura petrowi prevalence was lower overall but showed similar seasonal trends. Birds under approximately 10 wk of age were less likely to have high infection levels, and the population's age structure influenced infection dynamics in late summer. A significant co-infection association between A. pennula and O. petrowi suggests overlapping parasite incidence, which is expected given their shared intermediate hosts. Although the medicated feed demonstrated sustained effectiveness, treatment outcomes varied, likely due to climate conditions and bird behavior. These results support continued biannual treatments but emphasize the need for site-specific adjustments, such as extending pre-baiting periods, to enhance efficacy. Continued monitoring will refine treatment timing, enhance cost-effectiveness, and mitigate the impacts of helminths on bobwhite populations.