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Abstract
Integrated crop-livestock systems can restore ecosystem services like biological control and nutrient cycling to agroecosystems. However, the joint production of livestock and crops can pose food safety risks to consumers. Wild birds in particular have been identified as vectors of foodborne bacteria like Salmonella and Campylobacter to produce from livestock, while chickens are a large reservoir of bacteria in the US Southeast. Here, we consider the food safety risks of both wild birds and outdoor-access chickens on farms, while also describing the biological control services chickens can provide growers. We used a combination of bacterial cultures and PCRs to characterize bacterial prevalence in wild bird and chicken feces; this data was then used in several different statistical models to connect food safety risks to livestock presence, farm management, and wider landscape and weather variables. We used a DNA metabarcoding approach to characterize outdoor-access chicken diet and evaluate biocontrol potential of chickens. We found that Salmonella prevalence in wild birds was positively associated with livestock presence on-farm, although livestock were not the source of bacteria. In chicken feces, Campylobacter prevalence was positively associated with higher temperatures and the number of families of flies and plant phylogenetic diversity in chicken diet. This indicates that flies may be an important on-farm bacterial vector, and that chicken foraging behavior may increase the risk of encountering environmental bacteria. We found that chickens foraged very generally, eating a wide array of both arthropods and plants, but we were unable to definitely conclude whether chickens had a net positive, negative, or neutral impact on insect pests and weeds. Growers may be able to better manage food safety risks while still gaining the benefits of livestock ecosystem services by managing bacterial vectors like wild birds and flies. In a brief literature review of management options for growers, we found that physical deterrents and barriers were more effective than scaring deterrents for managing wild birds; likewise, physically preventing flies and other insects from entering livestock areas has been shown to effectively reduce food safety risks.