With the possibility of increased checking and testing for sulfa residues, producers may want to look at some of the new on-farm testing producers that are becoming available. The present tolerance level, set by the FDA's Center for Veterinary Medicine, is based on short-term toxicological studies with rats and dogs fed high levels of sulfonamides. Some of the animals in these studies developed thyroid toxicosis, which in one study progressed to thyroid carcinomas. The 0.1 ppm tolerance level, however, provides at least a 2,000-fold safety margin for humans. Another concern is for the small percentage of humans hypersensitive to sulfa drugs.
Sulfa also poses potential risks to people who continuously handle and mix medicated feed.
Swine housed on solid floors that allow accumulation of urine are more likely to experience recycling of sulfa than swine housed on slotted floors. Following sulfa withdrawal, move pigs to a clean pen or thoroughly clean the pen at the time of withdrawal. These pens need to be cleaned daily for two to three days following withdrawal. Don't let pigs have access to manure in trucks or holding pens or places where other sulfa-treated hogs were kept. Avoid using pens where pools of urine are allowed to form.