Depending on the shape of the feeder, considerable amounts of a medicated feed could remain in a feeder that appears to be empty. Addition of new feed may dislodge part of the old feed, making it available to the livestock using the feeder. Because of this characteristic, feeders should be completely emptied, then visually inspected for residual feed whenever changes are made in kinds or levels of animal drugs or to nonmedicated feed. Drop or floor feeding systems are less likely to cause contamination because residual feed is minimized. Feed allowed to build up in corners of pens due to overfeeding may be a potential source of residues.
Segregation can occur in ingredients and in mixed feeds.
In ingredients, it is the separation of certain fractions or particles from the remainder of the material. In mixed feeds, segregation is separation of one or more ingredients, or fraction of an ingredient. Partial remixing may occur during handling and processing operations, reducing the overall segregation effect on the finished feed. Table 1 lists some of the more common sites for segregation of mixed feed. Note that these are all subsequent to the mixing equipment.