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
Generated Summary
This review article examines the evolution of animal feeding practices in the United States over the past century, focusing on the potential impacts of animal feed ingredients on human health. It investigates the shift from small, family-owned farms to large-scale, concentrated animal feeding operations (CAFOs) and the subsequent modifications to animal feeds. The research explores the presence of various agents in animal feed, including rendered animals, animal waste, antibiotics, organoarsenicals, and the resulting biological, chemical, and other etiologic agents. The study employs a review of published veterinary and human-health literature, along with proceedings from animal feed workshops, to analyze the potential adverse human health impacts associated with these practices. The methodology includes the extraction of data from peer-reviewed articles and books identified through PubMed, Agricola, and databases from the U.S. Department of Agriculture, Food and Drug Administration, and Centers for Disease Control and Prevention. The aim is to assess the risks associated with current animal feeding practices and address data gaps that prevent comprehensive assessments of human health risks.
Key Findings & Statistics
- In 2003, the U.S. per capita consumption of total meats (including beef, pork, veal, lamb, poultry, fish, and shellfish) was 90.5 kg/year.
- In 2004, over 120 million tons of primary animal feed were produced in the United States.
- In the same year, the United States exported nearly $4 billion worth of animal feed ingredients.
- It is estimated that 17,500 U.S. animal feed dealers distribute the final feed products to individual feeding operations.
- The USDA estimated that > 4 million metric tons of rendered animal products were used as animal feed ingredients in 1984.
- In 2003, it was estimated that approximately 1 million tons of poultry litter were produced annually in Florida, and an estimated 350,000 tons of this litter were available for use in feed.
- In 2003, the rendering industry produced > 8 million metric tons of rendered animal products.
- Data collected by the USDA in 1984, estimated that > 4 million metric tons of rendered animal products were used as animal feed ingredients.
- In a study by Lynn et al. (1998), 30.1% of 209 samples of cattle feed collected from 13 dairies, 1 calf research facility, and 4 feed mills were positive for E. coli.
- Dargatz et al. (2005) found that 38.7% of 514 E. coli isolates were resistant to cephalothin, 24.7% were resistant to ampicillin, 16.6% were resistant to cefoxitin, and 12.1% were resistant to amoxicillin/clavulanic acid.
- In the same study, the authors also detected multiple antibiotic-resistant E. coli and Salmonella spp.
- Eighty-five percent of all feed ingredients sampled contained bacteria resistant to one or more of the following four antibiotics: ampicillin, amoxicillin, clavulanic acid, and cephalothin.
- Based on the assumptions that food-production animals are the source of 95% of human nontyphoidal Salmonella cases, it has been estimated that approximately 134,000 cases of human nontyphoidal salmonellosis could be attributed to contaminated animal feed each year (Angulo 2004).
- Levels (mean ± SD) of PCBs and dioxins detected in contaminated animal feed were 1658.4 ± 23584.4 ng/g of fat and 2319.8 ± 3851.9 pg international toxic equivalents (I-TEQs)/g of fat.
- Easton et al. (2002), detected total PCBs at mean concentrations of 51,216 pg/g and 5,302 pg/g in farmed and wild-caught salmon, respectively, and a mean concentration of 65,535 pg/g in commercial salmon feed.
Other Important Findings
- Animal feed ingredients include ingredients ranging from rendered animals and animal waste to antibiotics and organoarsenicals.
- 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.
- The U.S. animal feed industry is the largest producer of animal feed in the world.
- Feed mills combine plant- and animal-based feed ingredients to produce mixes designed for specific animal species.
- Rendering plants transform slaughter by-products and animals that are unsuitable for human consumption into animal feed products.
- Specific feed ingredients vary depending upon the animal (i.e., poultry, swine, cattle).
- Antibiotics are administered at nontherapeutic levels in feed and water to promote growth and improve feed efficiency.
- Roxarsone (4-hydroxy-3-nitrobenzenearsenic-acid) is administered to feeds at concentrations ranging from 22.7 g/ton to 45.4 g/ton.
- The most commonly used organoarsenical, roxarsone is administered to feeds at concentrations ranging from 22.7 g/ton to 45.4 g/ton to promote growth and improve feed efficiency.
- Metal compounds are also administered in animal feeds, and the compounds currently added to both swine and poultry feeds that are particularly concerning from a public health perspective are organoarsenicals.
- Animal feed often contains bacteria, including Salmonella spp. and E. coli, which can lead to human infections.
- The study highlights the use of antibiotics in animal feed and its role in contributing to antibiotic resistance in bacteria.
- The study mentions the presence of prions in animal feed, which are associated with the risk of BSE (Bovine Spongiform Encephalopathy), commonly known as mad cow disease, and its potential impact on human health.
- The document discusses the presence of mycotoxins, such as aflatoxins, ochratoxins, and fumonisins, in animal feed and their potential health impacts.
- Dioxins and PCBs are also mentioned as unintentional contaminants of animal feed.
- The study emphasizes the need for integrated veterinary and human health surveillance systems and increased collaboration among feed professionals, animal producers, and veterinary and public health officials.
Limitations Noted in the Document
- The study acknowledges significant data gaps that prevent comprehensive assessments of human health risks associated with animal feed practices.
- Limited data are collected at the federal or state level concerning the amounts of specific ingredients used in animal feed.
- There are insufficient surveillance systems to monitor etiologic agents “from farm to fork.”
- The authors state that data concerning the specific amounts of rendered animal protein that are used in animal feed are difficult to obtain because the information is neither routinely collected at the federal or state level nor reported by the rendering industry.
- No national data exist on the total amounts of animal waste included in animal feeds.
- The FDA does not officially endorse the use of animal waste in feed.
- The document indicates a lack of comprehensive data on the extent of mycotoxin contamination in feedstuffs.
- The study recognizes the challenges in determining whether other human food-borne bacterial illnesses besides those caused by S. enterica serotype Agona are associated with animal feeding practices.
- There are insufficient data to determine the percentage of antibiotic-resistant human bacterial infections that are attributed to the non-therapeutic use of antibiotics in animal feed.
- Little research has been conducted to determine whether the use of organo-arsenicals in animal feed, which can lead to elevated levels of arsenic in meat products, contributes to increases in cancer risk.
Conclusion
The review underscores the profound transformation in animal feeding practices in the United States, shifting from traditional, smaller-scale farming to large-scale, concentrated operations. This transition has introduced significant changes in animal feed formulations, with ingredients ranging from rendered animals and waste products to antibiotics and organoarsenicals. These changes are associated with the presence of various contaminants and agents in animal feed. The study highlights the critical need for increased funding for integrated veterinary and human health surveillance systems and the importance of collaboration among feed professionals, animal producers, and public health officials. It emphasized the potential adverse health impacts associated with animal feed, highlighting the need for rigorous epidemiologic studies and risk assessments to determine the extent to which human health risks are associated with animal feeding practices. The study acknowledges the substantial evidence linking U.S. animal feeds to contamination with human foodborne bacterial pathogens. The conclusions underscore the need for enhanced surveillance systems and a comprehensive approach to mitigate risks and ensure the safety of animal-based food products. The reliance on existing evidence, primarily from isolated case reports and outbreaks, underlines the significant data gaps and the need for more comprehensive and integrated systems to monitor and address the impact of animal feeding practices on public health. The lack of comprehensive data and the limitations in current surveillance make it difficult to fully assess the impact of these practices, highlighting the necessity for improved monitoring and a proactive approach to address the risks associated with animal feed.