Grazing management drives pathogen presence in surface- and ground-waters from beef cattle farms

Pathogens associated with livestock have the potential to impair nearby surface waters and groundwater through runoff and infiltration, endangering both human and animal health. As the livestock sector is growing globally, improving farm management is essential for protection of water resources. We intensively studied nine beef cattle farms over three grazing seasons to understand what farm management factors and environmental conditions contribute to the contamination of surface water and groundwater on and adjacent to the farms. We collected 103 groundwater and 146 surface water samples using dead-end ultrafiltration (n = 84) and passive samplers (n = 62) and monitored for Giardia, Cryptosporidium, pathogenic Escherichia coli, Salmonella Campylobacter and traditional microbial indicator organisms. While antecedent rainfall was often correlated with pathogen presence in water sources, grazing intensity (paddock resting days, total days grazing, and stocking density) more often drove pathogen presence in surface water and groundwater. For example, Cryptosporidium was more likely to be detected in surface water near conventionally grazed farms than rotationally (OR: 4.32; 95% CI: 1.56 - 13.05) and the odds of detecting Giardia in groundwater decreased with increased paddock resting days (OR: 0.79, 95% CI: 0.55 - 0.99). All groundwater sources were positive for pathogens and indicator organisms; an important finding given that public health guidelines indicate that these organisms should not be present in drinking water. Overall, variables associated with grazing management (including grazing intensity and duration) emerged as influential factors in pathogen presence in surface- and ground-waters more frequently than precipitation.