Potential for pathogen transfer from hog manure fertilizer to grazed cattle and groundwater

Hog manure can contain pathogenic bacteria such as Salmonella, Escherichia coli and Yersinia enterocolitica that may increase the risk of human illness if manure is used as fertilizer. The objective of this work was to investigate whether it could be demonstrated that Salmonella, E. coli and Y. enterocolitica naturally present in hog manure, can be transferred to cattle grazing on fields previously fertilized with manure. Trials were conducted over two summer seasons. Hog manure was applied via splash plate at a calculated rate of 61.8 or 123.6 kg of available N/ha to each of 4 plots totalling 16.2 ha. An equal area, divided into two plots, served as a control without manure. Fecal samples were taken directly from 60-80 beef cattle each year, and cattle were divided into groups and introduced on pasture plots. Animals were removed or additional Salmonella, and Y. enterocolitica negative cattle were added to the fields in response to vegetation growth. There were 40-109 cattle on manured fields and 16-20 on control fields. The interval between manure application and cattle introduction ranged from 10-30 d. Fecal samples were taken monthly for 3 months. Soil and plant samples were taken before and 1-24 d after manure application. All hog manure, soil, forage and cattle fecal samples were negative for Y. enterocolitica in both years of the trial. Two thirds (2004) and 100% of hog manure samples (2005) were Salmonella positive each year. Twenty-nine Salmonella Krefeld and 17 Salmonella Derby cultures were isolated from the hog manure. Six Salmonella Typhimurium cultures were isolated from the vegetation up to 14 d after manure application. All isolates of each serovar were the identical serotype. Salmonella was not recovered from soil and was absent from the cattle fecal samples for the entire length of the study. Hog manure had E. coli levels of 4-5 log CFU/g and the organism was detected on vegetation 1-2 d after manure application. E. coli was not recovered from vegetation before cattle were grazed. Transfer of E. coli from hog manure to soil and cattle was examined by genetic fingerprinting (RAPD) of isolates. DNA fingerprints were compared one to the other using ClustanGraphics 7 software. No E. coli DNA fingerprints from hog manure were in common with genomic fingerprints of E. coli isolated from soil. One E. coli DNA fingerprint from hog manure was identical to one E. coli fingerprint from cattle and this was not considered to be a statistically significant observation (Fisher's Exact test, p < 0.001). During this study, Salmonella and E. coli present in hog manure did not appear to have been transferred to cattle grazing on the manure-treated pasture. E. coli was recovered in water from one background well and two wells on the experimental site before manure application in 2005 and from one well during the July (2005) sampling period. Salmonella serovars (Worthington and Manhattan) different from those in the hog manure were recovered from water in four wells 20 d after manure application in the fall of 2005.