Avoiding Drug Carryover During Feed Processing and Delivery, Part 1

Avoiding Drug Carryover During Feed Processing and Delivery Drug carryover is a form of feed contamination that may result when the substance in question has been transferred (carried) from an acceptable location or feed to an unacceptable location or feed. Carryover of an animal drug can occur during feed processing, handling, or delivery. The Food and Drug Administration's (FDA) Good Manufacturing Practices (GMPs) provide guidance for medicated feed manufacturers to ensure their products meet the identity, strength, and quality standards that they should with respect to their drug content.

These regulations stipulate adequate procedures be established and followed for all equipment used in the production and distribution of medicated feeds to avoid unsafe contamination of medicated and nonmedicated feeds. Carryover of a Category II drug (one which requires a withdrawal period) into a finishing ration may result in a tissue-residue problem in meat animals. Producers experiencing this problem in their market animals may incur significant financial loss. Carryover of either a Category I drug (one which does not require a withdrawal time) or a Category II drug into a batch of feed intended for an off-label species may create serious problems.

For example, carryover of monensin from cattle feed to horse feed may kill the horse. The intent of this bulletin is to provide feed manufacturers, whether a commercial mill operator or an onfarm feed manufacturer, information that will help them avoid drug carryover. This information should help feed processors improve their product quality, reduce the likelihood of feed contamination, and help ensure safe meat, milk, and eggs destined for human consumption.

Risk Assessment Meat, milk, and egg producers have many options for obtaining a complete feed ration, as depicted in Figure 1. It is the responsibility of the feed processor (whether commercial or on-farm) to ensure that the correct amount of the desired drug is properly incorporated and that no cross-contamination of an unwanted/unspecified drug is present in that feed. Whether the manufacturing system is simple or complex, it is possible to avoid drug carryover by following the GMPs. The type of drug (Category I or II), number of species, and feed delivery system determine the degree of risk associated with drug carryover.

Feed processors who manufacture products for one species and use only Category I drugs experience the least amount of risk associated with cross-contamination and tissue residue. Since there is no withdrawal time associated with this product, it may be used until the time of slaughter. The individual who uses a Category II drug can avoid carryover and tissue residue problems by using separate delivery systems for these feeds and by sequencing, flushing, and cleaning feed processing equipment. Mills that produce feed for multiple species experience an increased risk of crosscontamination by medicated articles (either Category I or II) than mills manufacturing products for one species. When changing feed rations from one species to the next the risk of cross-contamination is minimized through sequencing, flushing, and equipment cleanout of feed processing and delivery equipment.

Causes for Carryover Drug carryover may occur for many reasons as outlined in Table 1. Significant amounts of the drugs or medicated feed may remain in the production system and contaminate the following batches of feed. It may occur in one piece of equipment, or it may result from a combination of residues throughout the entire system. Once the source of carryover is known, corrective action can be taken. Often, adjustment of equipment will markedly relieve the problem. Repairs, remodeling, or replacement of worn components may be necessary. A few of the more common corrective measures are listed in Table 2.

Table 1. Sources of Carry-over