Sampling for salmonella in feed began in the late 1950's, as an agreement between SVA and the feed industry. Recent studies had then shown that salmonella could spread from feed to food-producing animals, a fact that was not previously known. The control of feed later became an important part of the successful Swedish salmonella control of food-producing animals, a measure that was not taken in other countries. The realization that raw feed material may contain salmonella initiated early control measures for mainly imported animal feedstuffs. In 1991, a new control program for salmonella in feed was established based on HACCP (Hazard Analysis Critical Control Points) principles. This program became mandatory in 1993, when it was introduced in the Regulations from the Board of Agriculture.
The responsibility of the feed manufacturer
The feed manufacturer is responsible for producing a salmonella-free feed. In the control programme, the focus is on control of ingredients, the heat treatment process and preventive measures to eliminate post-process recontamination of heat treated feed. The purpose is to ensure the absence of Salmonella in the production lines and the feed mill environment. It is legally required that all poultry feed has to be heat-treated. The same legal requirement does not exist for other animal feed. Today, however, almost all feed is heat-treated - even for cattle and pigs. The control of feed production is under the responsibility of the Board of Agriculture, who is also responsible for unannounced inspections.
Feed materials are classified according to which risk for salmonella contamination they pose: the highest risk class (S1) only includes feed material of animal origin e.g. fish meal. Risk class S2 includes feed material of vegetable origin – soybean meal and some rapeseed products and S3 includes rice and some rapeseed products*. All imported feed materials that are classified as S1, S2, and S3 must be sampled for salmonella. The commodities are often sampled at the European point of entry. The rationale behind this is to have the test result available when the product arrives in Sweden, so proper action can be taken if the consignment is Salmonella contaminated.
* SJVFS 2018:33 appendix 4
Manufacturing of feed materials
If the produced raw feed materials are classified as risk class S2 or S3, the feed company is obliged to have a salmonella control program to ensure that the manufactured feed material is safe to use.
Process control in feed mills
According to national legislation, environmental sampling for control of Salmonella contamination (HACCP) has to be conducted on a weekly basis. Following five control points in the processing line in feed mills that manufacture compound-feed for food-producing animals are sampled:
- Top of bin for final feed
- Room for pellet coolers
- Top of pellet cooler
- Dust from the aspiration system (filter)
- Intake pit/bottom part of elevator for feed materials.
At these critical control points dust samples or scrapings are collected.
When poultry feed is produced, a minimum of one environmental sample has to be taken at each of the above five control points and checked for the absence of salmonella. When only non- poultry feed is produced the corresponding requirement is limited to control points 1 and 5. These samples are taken by the operator and all samples have to be sent to the National Veterinary Institute (SVA) for analysis and to control that the number of samples is in accordance with the legislation.
However, most operators normally take additional environmental samples to ensure that their feed does not contain salmonella. These samples can be analyzed at any accredited laboratory of choice. However, all isolates of salmonella (no matter where they are found) must be sent to SVA for serotyping.
Compound feeding stuffs that are traded into Sweden destined for feeding of cattle, pigs, poultry or reindeer have to be tested for Salmonella in accordance with the same testing principles as other feed material.
When salmonella is detected
If Salmonella is detected in the weekly monitoring, a larger sampling is made immediately in the production line and different measures are then undertaken depending on the result. If Salmonella is found before heat treatment, the contaminated part of the production line is thoroughly cleaned and disinfected, usually by dry cleaning, followed by disinfection. If Salmonella is found after heat treatment, the feed mill has to be thoroughly cleaned and disinfected. Environmental sampling must show negative results before production is resumed.
According to national legislation, a feed operator has to take actions when Salmonella has been detected in the herd of a customer. This includes monitoring by sampling of the production line from which the feed to the customer was delivered and normally the dispatch samples from feed delivered to the customer are checked as well.
Salmonella positive findings in feed material are usually treated with organic acids, such as formic acid. After acid treatment the feed material has to be tested negative for Salmonella before being used in the feed production. Feed materials that have been treated with acid are only allowed to be used in feed that is supposed to be heat treated.
In premises where products are derived from industrial processing and Salmonella has been detected, a larger sampling schedule is undertaken in the production line. If Salmonella is found the contaminated part of the production line is thoroughly cleaned and disinfected, usually by dry cleaning, followed by disinfection.