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Amy R. Sapkota,^1,2 Lisa Y. Lefferts,^1,3 Shawn McKenzie,¹ and Polly Walker¹

¹Johns Hopkins Center for a Livable Future, Bloomberg School of Public Health, Baltimore, Maryland, USA; ²Maryland Institute for Applied Environmental Health, College of Health and Human Performance, University of Maryland, College Park, Maryland, USA; ³Lisa Y. Lefferts Consulting, Nellysford, Virginia, USA

Abstract
Objective: Animal feeding practices in the United States have changed considerably over the past century. As large-scale, concentrated production methods have become the predominant model for animal husbandry, animal feeds have been modified to include ingredients ranging from rendered animals and animal waste to antibiotics and organoarsenicals. In this article we review current U.S. animal feeding practices and etiologic agents that have been detected in animal feed. Evidence that current feeding practices may lead to adverse human health impacts is also evaluated.

Data sources: We reviewed published veterinary and human-health literature regarding animal feeding practices, etiologic agents present in feed, and human health effects along with proceedings from animal feed workshops.

Data extraction: Data were extracted from peer-reviewed articles and books identified using PubMed, Agricola, U.S. Department of Agriculture, Food and Drug Administration, and Centers for Disease Control and Prevention databases.

Data synthesis: Findings emphasize that current animal feeding practices can result in the presence of bacteria, antibiotic-resistant bacteria, prions, arsenicals, and dioxins in feed and animal-based food products. Despite a range of potential human health impacts that could ensue, there are significant data gaps that prevent comprehensive assessments of human health risks associated with animal feed. Limited data are collected at the federal or state level concerning the amounts of specific ingredients used in animal feed, and there are insufficient surveillance systems to monitor etiologic agents "from farm to fork."

Conclusions: Increased funding for integrated veterinary and human health surveillance systems and increased collaboration among feed professionals, animal producers, and veterinary and public health officials is necessary to effectively address these issues.

Key words: animal feed, animal waste, concentrated animal feeding operations, fats, human health effects, nontherapeutic antibiotics, rendered animals, roxarsone, zoonoses. Environ Health Perspect 115:663–670 (2007) . doi:10.1289/ehp.9760 available via http://dx.doi.org/ [Online 8 February 2007]

Address correspondence to A.R. Sapkota, Maryland Institute for Applied Environmental Health, College of Health and Human Performance, University of Maryland, College Park, 2306 HHP Building, College Park, MD 20742 USA. Telephone: (301) 405-2438. Fax: (301) 405-8397. E-mail: amy@amysapkota.com

We thank R. Lawrence, E. Silbergeld, and S. Joseph for providing many insightful comments.

This research was funded by the Johns Hopkins Center for a Livable Future, Bloomberg School of Public Health.

The authors declare they have no competing financial interests.

Received 25 September 2006 ; accepted 8 February 2007.