A drug added to a target feed for a certain purpose appears in a non-target feed for various reasons during processing, that is, cross-contamination. Feed cross-contamination exists in all feed mills, and reducing feed cross-contamination is an important measure to ensure feed safety. The author now analyzes the causes of drug cross-contamination from the perspective of feed processing, and puts forward suggested improvement measures for the reference of feed manufacturers.

1 Analysis of the causes of pollution in feed processing

 Drug contamination of feed may occur during feed processing, transport and storage. Among them, the pollution during processing mainly includes the following aspects:

1.1 Dust collection system In the processing workshops of large and medium-sized feed factories, dust collection systems are distributed in each main link in the processing process, the purpose is to reduce the dust generated in the processing link and purify the production environment. The collected dust is generally returned to the feed from an economical point of view, but the delayed return of dust or the unreasonable design of the dust collection system can lead to excessive absorption of the pharmaceutical additives.

 1.2 Batching system Accurate batching is the premise and guarantee of strictly implementing the production formula. Once there is an error in the measurement of the pharmaceutical additive and it is not detected in time, the follow-up section is irreparable, which will bring serious pollution.

 1.3 Mixing system The mixing process is the process of uniform distribution of various components, and it is also the main link of drug pollution. The reasons are: the setting of the mixing time is unreasonable, and the expected mixing effect is not achieved, resulting in uneven mixing or excessive mixing; improper design of the mixer, resulting in incomplete discharge and residual feed; the material mouth of the mixer cannot be tightly closed Or the gasket is damaged to cause leakage; the feed viscosity is large (due to the addition of molasses and grease) or it is attached to the inner wall, top and air return pipe of the mixer due to static electricity.

1.4 Buffer silo The buffer silo is an equipment that balances the processing capacity among the equipment to facilitate continuous production. However, if the volume of the buffer tank is too small, the design is unreasonable, or the adhesion is formed due to static electricity or moisture, the residual feed cannot be completely removed, and drug contamination may also occur.

 1.5 Conveyor Excessive conveying distance, unreasonable design or operation of horizontal conveying equipment, too large bottom clearance, and feed adhesion due to static electricity or moisture may lead to feed residues.

 1.6 Bucket elevator The drug residue caused by the bucket elevator is generally very small, but static electricity, humidity and excessive viscosity will also leave residues on the lifting bucket or base, causing pollution.

 1.7 Silo The drug pollution caused by the silo is mainly caused by unreasonable design or operation (slope less than 60 degrees). In addition, the undulations inside the silo, incomplete silo removal, and alternate use of the same silo for medicated and non-medicated feeds can all lead to drug contamination in the feed.

 1.8 Production sequencing Production sequencing is the order in which different types or different formula feeds are produced. Due to operating technology, production technology, production equipment and other reasons, the feed products produced in the previous batch will have an impact on the products produced later, so incorrect production sequencing is also the cause of drug contamination.

2 How to reduce or prevent contamination in processing

2.1 Production process design When designing the feed processing process, the conveying distance should be shortened as much as possible, the horizontal conveying equipment should be used less, and the form of distributor and self-flow conveying should be used as much as possible. For horizontal conveying equipment, scraper conveyors with automatic removal function should be used as much as possible. Under the condition that the process requirements are met, the number of material lifting times and the number of transition hoppers should be minimized. The suction and dust removal system should be equipped with an independent air network as much as possible. The dosing of the compound premix is arranged in the upper part of the mixer.

2.2 Sequence of feed production - The general principle is to produce feed without drugs first, and feed with drugs. Feeds with the same drug or feed used by animals of the same species should be processed together, and those with high drug content should be processed first. Feed, reprocess feed with low drug content; for the same type of animal use drug-containing feed, first produce feed that is not restricted by the withdrawal period, such as sow lactation (pre-stage) feed, etc., and then produce the feed restricted by the withdrawal period ; When the sales volume of a certain medicated feed is much higher than that of the non-medicated feed, it may be considered to set up a completely separate special production line to minimize the possibility of cross-contamination. Reasonable sorting should be reflected in the entire processing system, that is, from the warehouse to be crushed to the end of the finished product warehouse.

2.3 Static adhesion In order to eliminate static electricity, you can install a ground wire on the equipment to buy non-static premix; add liquid raw materials to control dust and reduce static electricity; install a vibrator on the part where the feed is easily attached to shake off the attachments.

2.4 The dust collection system correctly designs the air flow rate and flow pressure of the dust collection air net, and cleans the dust in the entire system in time; uses liquid raw materials to reduce dust; the dust collected during the production of medicated feed should be discarded or played back to the next page. batches of feed containing similar drugs.

2.5 The mixer should use a mixer with high uniformity for the feed containing medicine, or adjust the spacing between the mixing spiral belt, mixing paddle and bottom plate of the existing mixer. The easiest way to do this is to install plastic brushes or air-sweep nozzles on the mixing helix to remove residue. The correct feeding sequence and time are also critical, generally when the mixer is full of 1/2 to 3/4 the drug is fed.

2.6 Bucket elevator Adjust the base of the bucket elevator, reduce the height of the hopper, so that it can be cleaned more cleanly; install the air cleaning nozzle, and the inner surface and transition parts must be clean and smooth.

2.7 The design of the silo should be scientific; when the type of feed stored is changed, it should be checked and cleaned; an oscillator should be installed to remove the residue.

2.8 Conditioner, granulator and dryer The residue in the dryer can be solved as long as you pay attention and remove it in time. Residues in conditioners and granulators can be solved by "rinsing". "Flushing is the use of a certain amount of a certain raw material, such as corn meal, soybean meal or wheat bran, etc., to take away the residues of medicated feed or animal-derived feed on the equipment." Flushing can also start from the silo to be crushed and run through the entire Production Process. Used flushing material can be properly labelled, stored, and reused in the production of suitable feed.

Feed safety is a systematic project. In addition to the pollution in feed processing, a sound quality management system and system is also an important aspect that affects feed safety. Feed processing enterprises should pay attention to it in many aspects.