Evaluating flushing procedures to prevent nicarbazin carryover during medicated feed manufacturing

Carryover of medicated feed additives between batches of feed can potentially result in harmful drug residues in the edible tissues of food-animals. Flushing the equipment with an ingredient, such as ground grain, is one method used to remove any residual medicated feed from the system. It is generally recommended that the quantity of flush used be between 50 and 100 g/kg of the mixer's capacity. However, there is little data that supports this recommendation. Therefore, an experiment was conducted to determine the minimum quantity of flush material required to prevent drug carryover; and to quantify the interrelationship between flush size and drug concentration. The feed medicated with nicarbazin (Nicarb 250 g/kg®; 00.125 g/kg) was manufactured and conveyed from the mixer, through a drag conveyor and bucket elevator, and placed into a finished product bin. The system was then flushed using ground corn in the amount of 25, 50, 100, 150, or 200 g/kg of the mixer's capacity (454.5 kg). Subsequently, a non-medicated diet was conveyed through the system and samples were collected and analyzed for nicarbazin. No differences were detected among the flush treatments, and all treatments were effective in reducing nicarbazin carryover to less than 2.2 mg/kg to the non-medicated diet. Collectively, these studies demonstrate that existing flushing guidelines meet or exceed what is required to prevent carryover of medicated feed additives.