The effect of sewage irrigation on safety and hygiene of forage crops and silage

Abstract

The aim was to evaluate the safety of summer forage crops in Israel irrigated with secondary-treated sewage water. Nitrates levels and the incidence of Escherichia coli and Salmonella in corn and sorghum intended for silage were determined, as well as the fates of E. coli and added nitrates, during ensiling. E. coli and Salmonella were found in 9 and 1, respectively, out of 41 samples of forage crops that had been irrigated with sewage water. E. coli disappeared from the silage following the decrease in pH, but was found in decaying parts of commercial silages in which the pH increased. The concentration of nitrates in summer forage crops was usually below the critical level, which is toxic to cattle. The lower parts of the plants contained more nitrates than the other parts. The highest levels of nitrates were found in plants, which were irrigated with captured flood water. The conclusions of this study are that nitrates, E. coli and Salmonella from forage crops irrigated with sewage water are not likely to pose a health risk to cattle if the ensiling process is adequate.