A review of animal feed ingredients and their potential impacts on human health

What do we feed to food-production animals?

A review of animal feed ingredients and their potential impacts on human health

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]

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Animal-based food products derived from cattle, swine, sheep, poultry, and farmed fish constitute a significant portion of the current U.S. diet. 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 [U.S. Department of Agriculture (USDA) 2005a]. Data from animal-production researchers demonstrate that the quality of these products is directly related to animal feeding practices (Capucille et al. 2004; Gatlin et al. 2003; Zaghini et al. 2005). Therefore, given the high consumption of animal-based food products in the United States, the ingredients used in animal feed are fundamentally important in terms of both the quality of the resulting food products and the potential human health impacts associated with the animal-based food-production chain.

In the early 1900s, animals produced for food in the United States were raised on small family farms where cows predominantly grazed on pasture and young chickens were fed primarily a corn-based diet (Erf 1907). However, in the past 60 years, farms and animal feed formulations have undergone significant changes. Small family-owned and -operated farms have been replaced almost entirely by a system of large-scale operations where individual farmers contract with vertically integrated corporations. High rates of food production have been achieved through these systems in which the scale of operations requires the high throughput generation of animals for processing. Animals are raised in confinement and fed defined feeds that are formulated to increase growth rates and feed-conversion efficiencies. These present day animal feeds contain mixtures of plant-based products, as well as other ingredients ranging from rendered animals and animal waste to antibiotics and organoarsenicals. The inclusion of these ingredients in animal feeds can result in the presence of a range of biological, chemical, and other etiologic agents in feed that can affect the quality and safety of animal-based food products and pose potential risks to human health.

Since December 2003, when the first U.S. case of bovine spongiform encephalopathy (BSE) was identified in a dairy cow in Washington State, there has been increased attention from veterinary and public health professionals regarding the quality and safety of U.S. animal feed, as well as the safety of subsequent animal-based food products. Yet, the focus of such attention is often limited to one particular facet of animal feed and its associated animal or human health effect (i.e., the impact of rendered animals in feed formulations on the risk of BSE, the impact of bacterial contamination of animal feed on human bacterial illnesses). However, to begin to understand the broad range of potential human health impacts associated with current animal feeding practices, it is necessary to examine the full spectrum of feeding practices and assess their potential human health implications collectively.

In this article we review U.S. animal feed-production practices; animal feed ingredients; and biological, chemical, and other etiologic agents that have been detected in animal feed. In addition, we evaluate evidence that current feeding practices may be associated with adverse human health impacts, and address the data gaps that prevent comprehensive assessments of human health risks associated with animal feed.

U.S. Animal Feed Production

The U.S. animal feed industry is the largest producer of animal feed in the world (Gill 2004). In 2004, over 120 million tons of primary animal feed, including mixes of feed grains, mill by-products, animal proteins, and microingredient formulations (i.e., vitamins, minerals, and antibiotics) were produced in the United States (Gill 2004). In the same year, the United States exported nearly $4 billion worth of animal feed ingredients (International Trade Centre 2004).

The structure of the U.S. animal feed industry is complex, with a multitude of industries and individual producers contributing to the production, mixing, and distribution of feed ingredients and complete feed products. However, there are a few firms that play principal roles in the manufacture of U.S. feeds, including feed mills, rendering plants, and protein blenders [General Accounting Office (GAO) 2000]. Feed mills combine plant- and animal-based feed ingredients to produce mixes designed for specific animal species (GAO 2000). Rendering plants transform slaughter by-products and animals that are unsuitable for human consumption into animal feed products using grinding, cooking, and pressing processes (GAO 2000; National Renderers Association Inc. 2005a). Protein blenders mix processed plant- and animal-based protein ingredients from many sources into animal feeds (GAO 2000). Once animal feed ingredients are mixed, an estimated 17,500 U.S. animal feed dealers distribute the final feed products to individual feeding operations (Feedstuffs 2005).

Animal Feed Ingredients and Feeding Practices

Animal feed ingredients that constitute complete feed products are derived from a multitude of raw materials of plant and animal origin, as well as pharmaceutical and industrial sources. Specific feed ingredients vary depending upon the animal (i.e., poultry, swine, cattle); Table 1 provides an overview of feed ingredients that are legally permitted and used in U.S. animal feed. More specific information about feed ingredients listed in Table 1 is available in the Official Publication of the Association of American Feed Control Officials, Inc. (AAFCO), which is published annually (AAFCO 2004), and in Lefferts et al. (2006). In the present review we focus on feed ingredients listed in Table 1 that raise specific concerns for public health, including rendered animal products, animal waste, plant- and animal-based fats, antibiotics, and metals.

Rendered animal products. In 2003, the U.S. rendering industry produced > 8 million metric tons of rendered animal products, including meat and bone meal, poultry byproduct meal, blood meal, and feather meal (National Renderers Association Inc. 2005b). Most of these products were incorporated into animal feed. However, 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. The latest available data, collected by the USDA in 1984, estimated that > 4 million metric tons of rendered animal products were used as animal feed ingredients (USDA 1988). Oftentimes these ingredients are listed on animal feed labels as "animal protein products." Thus, it is difficult to discern precisely which animal protein products are included in a particular animal feed product (Lefferts et al. 2006).



by Amy R. Sapkota, Lisa Y. Lefferts, Shawn McKenzie, Polly Walker

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