Sanitary Status of 44 Hog Manures in Brittany: Comparison of the Effectiveness of Manure Treatments Based on the Levels of Indicator Bacteria and Two Pathogenic Bacteria

The hygienic performance of simple storage and biological treatment of manure was evaluated using effluents collected from 44 hog farms across Brittany, France. Analyses were carried out on raw manure, on the sludge stored after biological treatment and on the liquid phase stored in a lagoon after sludge settling or sludge dewatering. The effect of the treatments was evaluated on E. coli, enterococci, Clostridium perfringens, Salmonella and Listeria monocytogenes. Sequential feeding of manure maintained a high level of enteric bacteria in storage tanks regardless the duration of storage, and biological treatment only slightly reduced the concentration of enteric bacteria (average reduction in raw manure and sludge &88042.2 log10). Salmonella and L. monocytogenes were identified in raw manure (50% and 18.2% of samples, respectively), in sludge (14.8% and 11.1%), and in lagoons (8.0% and 24%), suggesting that there is still a sanitary risk after biological treatment of manure. Salmonella Derby and L. monocytogenes serotype 4b each accounted for 50% of the serotypes identified in the samples. There was no correlation between the presence of the two pathogenic bacteria and the size of the herd or the duration of manure storage. However, environmental conditions in the lagoons appeared to favor the presence of L. monocytogenes and hence a risk of disseminating this pathogen in the environment.