Large-scale, concentrated animal production methods now dominate animal husbandry. Animal feeds have been modified to include ingredients ranging from rendered animals and animal waste to antibiotics and organoarsenicals. This article reviews current U.S. animal feeding practices and etiologic (disease-causing) agents in animal feed.
Food-animal production in the United States has changed markedly in the past century, and these changes have paralleled major changes in animal feed formulations. While this industrialized system of food-animal production may result in increased production efficiencies, some of the changes in animal feeding practices may result in unintended adverse health consequences for consumers of animal-based food products.
Currently, the use of animal feed ingredients, including rendered animal products, animal waste, antibiotics, metals, and fats, could result in higher levels of bacteria, antibiotic-resistant bacteria, prions, arsenic, and dioxin-like compounds in animals and resulting animal-based food products intended for human consumption. Subsequent human health effects among consumers could include increases in bacterial infections (antibiotic-resistant and nonresistant) and increases in the risk of developing chronic (often fatal) diseases such as vCJD.
Nevertheless, in spite of the wide range of potential human health impacts that could result from animal feeding practices, there are little data collected at the federal or state level concerning the amounts of specific ingredients that are intentionally included in U.S. animal feed. In addition, almost no biological or chemical testing is conducted on complete U.S. animal feeds; insufficient testing is performed on retail meat products; and human health effects data are not appropriately linked to this information. These surveillance inadequacies make it difficult to conduct rigorous epidemiologic studies and risk assessments that could identify the extent to which specific human health risks are ultimately associated with animal feeding practices. For example, as noted above, there are insufficient data to determine whether other human foodborne bacterial illnesses besides those caused by S. enterica serotype Agona are associated with animal feeding practices. Likewise, there are insufficient data to determine the percentage of antibiotic-resistant human bacterial infections that are attributed to the nontherapeutic use of antibiotics in animal feed. Moreover, little research has been conducted to determine whether the use of organoarsenicals in animal feed, which can lead to elevated levels of arsenic in meat products (Lasky et al. 2004), contributes to increases in cancer risk.
In order to address these research gaps, the following principal actions are necessary within the United States: a) implementation of a nationwide reporting system of the specific amounts and types of feed ingredients of concern to public health that are incorporated into animal feed, including antibiotics, arsenicals, rendered animal products, fats, and animal waste; b) funding and development of robust surveillance systems that monitor biological, chemical, and other etiologic agents throughout the animal-based food-production chain "from farm to fork" to human health outcomes; and c) increased communication and collaboration among feed professionals, food-animal producers, and veterinary and public health officials.
Amy R. Sapkota, Lisa Y. Lefferts, Shawn McKenzie, and Polly Walker
>Johns Hopkins Center for a Livable Future, Bloomberg School of Public Health, Baltimore, Maryland, USA; >Maryland Institute for Applied Environmental Health, College of Health and Human Performance, University of Maryland, College Park, Maryland, USA; >Lisa Y. Lefferts Consulting, Nellysford, Virginia, USA