Review--animal waste used as livestock feed: dangers to human health.

Foodborne illness remains a common and serious problem, despite efforts to improve slaughterhouse inspection and food preparation practices. A potential contributor to this problem that has heretofore escaped serious public health scrutiny is the feeding of animal excrement to livestock, a common practice in some parts of the United States. In 1994, 18% of poultry producers in Arkansas collectively fed more than 1,000 tons of poultry litter to cattle, and the procedure is also common in some other geographic areas as a means of eliminating a portion of the 1.6 million tons of livestock wastes produced in the United States annually. While heat processing reliably kills bacterial pathogens, its use is limited by expense and other factors. Deep-stacking and ensiling are commonly used by farmers to process animal wastes, but the maximal temperatures achieved in stacked poultry litter are typically in the range of 43 to 60 degrees C (110 to 140 degrees F), below the inactivation temperatures of pathogenic salmonella and Escherichia coli species, and far below the USDA's recommended cooking temperatures of 71 to 77 degrees C (160 to 170 degrees F) for potentially manure-tainted meat products. In addition to the spread of potential pathogens, using animal wastes as feed presents the possibility that antibiotic-resistant bacteria may spread from one animal to another and that antibiotics or other chemicals may be passed between animals. Few research reports have addressed the safety of this practice, and those studies that have been published have generally been in controlled and artificial environments, rather than in on-farm conditions. Further microbiological studies are recommended to assess the extent of risk.