Animal & Veterinary
Exposure Scoring for Feed Contaminants – A Swine Feed Example
May 11, 2007
The goal of CVM’s Animal Feed Safety System (AFSS) is to develop and implement a comprehensive, preventive, risk-based program that prevents, reduces or eliminates the risks to animal and human health that can arise from hazards in animal feed. An integral part of this effort is the development of a relative risk-ranking method for all potentially toxic or deleterious biological, chemical and physical hazards in animal feed.
It is very important to note that this risk-ranking exercise is not intended for the estimation of risks associated with any one particular feed contaminant; instead, it is intended to be a tool for ranking of the relative risks of feed contaminants to aid FDA in setting priorities for allocating its resources in a risk-based manner.
Risk assessment may be thought of as answering four basic questions:
- What can go wrong? (Hazard Identification);
- What are the consequences? (Consequence Assessment or Hazard Characterization);
- How can it happen? (Exposure Assessment); and,
- What is the likelihood it would happen? (Risk Estimation).
At the September 12, 2006 public meeting the agency addressed the first question--the Hazard Identification step—by releasing a list of feed contaminants that are the initial focus of the risk-ranking exercise. At the same meeting the agency also addressed the second step—the assessment of the health consequences associated with the identified hazards—by explaining how it was going to develop Hazard Scores for chemical and microbiological feed contaminants.
Questions 3 (Exposure Assessment) is the subject of the May 22, 2007 public meeting.
Question 4 (Risk Estimation) will be the subject of one or more future AFSS documents and public meetings.
C. Exposure Scoring
The purpose of this document is to provide a brief overview of the risk-ranking approach, with primary focus on methods used to determine Exposure Scores (ES).
At the May 22, 2007 meeting, exposure scoring for swine feed will be presented as an example of how exposure to biological and chemical contaminants in feed will be determined for the AFSS relative risk-ranking model. We will identify three examples of swine feed (grower and finisher) and representative ingredients for each feed. We will estimate swine and human exposures to the following chemical and microbiological contaminants in the feeds: mycotoxins, pesticides, heavy metals, dioxins, PCBs, Salmonella enterica, E. coli 0157:H7 and other microbes.
Contaminant Levels in Feed Ingredients
For chemical contaminants, levels of each contaminant in ingredients used in each example swine feed will be determined from data collected under the agency’s Feed Contaminants Program and from the published scientific literature; these data will be augmented with expert opinion, as needed. When data on contaminant levels are available only for a broad, general category of feed ingredients (e.g., level of mycotoxins in corn and corn-byproducts), information on how an individual ingredient was processed will be used to help estimate the levels of contaminants in that ingredient (e.g., mycotoxins in Distillers Dried Grains derived from corn).
For microbial contaminants, data on the percentage of feed ingredients that test positive for the identified microbes will be used to estimate the likelihood of animal and human exposure to microbes. Although data on the levels of each microbe in animal feeds could be used to help estimate animal and human exposure to microbes, such data are not available for most microbes. Data on the percentage of feed ingredients that test positive for the identified microbes will be augmented by expert opinion, particularly for microbes other than Salmonella enterica and E. coli O157:H7. When data on the percentage of feed ingredients with microbes are available only for a broad, general category of feed ingredients (e.g., plants and plant by-products), information on how an individual ingredient (e.g., soybean meal) was processed will be used to help estimate the percentage of feed ingredients that test positive for the identified microbes.
- Contaminant Levels in Swine Feeds
Contaminant levels in the example swine feeds will be based on the levels of contaminants in the feed ingredients, adjusted for the level of each ingredient in the feed and the sensitivity of each ingredient to processes used in feed manufacture, such as pelleting. Adjustments to levels of contaminants in feeds consumed by swine will be made based on the effects storage, transport and feeding may have on the level of each contaminant in the feed fed to swine.
- Swine Exposure to Foodborne Contaminants in Feed
Swine foodborne exposure to chemical contaminants in feed will be determined by summing contaminant exposures from example feeds, and weighting for the duration of a pig’s exposure to each of the example feeds.
Estimation of swine foodborne exposure to the identified microbiological contaminants will be based on an assumption about the contribution of each microbe in feed to the overall rate of swine illness attributed to that microbe from all sources.
Human Foodborne Exposure to Contaminants in Swine Feed
For chemical contaminants, human foodborne exposure to contaminants in swine feed will be determined by the lifetime exposure of swine to levels of the contaminants, adjusted for 1) the likelihood the contaminant will bioaccumulate in the edible tissues and organs of swine and 2) for the amount of swine products consumed by humans during their lifetimes.
For microbiological contaminants, human exposure to contaminants in swine feed will be based on an assumption about the contribution of each microbe in swine feed to the overall rate of human illness attributed to that microbe from pork, and will largely be based on expert opinion due to the lack of specific data.