The results were published in the journal Food Microbiology.
Feed ingredients that have a high protein content are the most commonly contaminated raw materials and may introduce Salmonella into feed mills and into the feed mixing environment at pig farms, according to the authors.
“In recent years, most of the Salmonella positive findings from feed ingredients in Finland have been obtained from foreign protein-rich materials, such as soy,” the Finnish risk assessors noted.
The authors analysed the impact on the Salmonella risk from the diminishing proportion of these ingredients.
Risk analysis rationale
However, the relative proportion of Salmonella infections in pigs due to contaminated feed and the relative proportion of human cases from domestic pork are not high in Finland.
Thus, we asked Maria Rönnqvist, researcher, EVIRA, explained the trigger for the study.
“The Salmonella control program is costly and resource-demanding, which was the reason our Ministry of Agriculture and Forestry wanted that the risks, costs and benefits of the program are investigated. The risks were analyzed at Evira and the cost-benefit part of the project was done by natural resources institute, Luke.
“The other parts of the program - pork chain, beef chain, eggs, broilers - have been evaluated previously but the feed chain hadn't been. Pig farming is not very profitable in Finland at the moment, so we specially wanted to see whether it is cost efficient to continue such a heavy Salmonella monitoring program in pig feed chain.”
The results of the study showed that at the current low level of Salmonella in the country, the control programme is profitable, she said.
"As a relatively high share of the few cases of Salmonella in pigs are feedborne, feed should be kept Salmonella-free if possible. In countries where Salmonella prevalence in pigs is currently high - more than 10% or so - feed as a source is less significant, but when the level in pigs decreases the impact of feed will probably be more significant in those countries also.”
The study concluded that any move to reduce the strict level of controls on Salmonella in the pig feed production chain in the country could cause an unwanted increase in human cases.
“The introduction of Salmonella to the farm environment can occur via the purchase of new production animals as well as via contaminated feed and feed materials, infected rodents, birds, insects, pets and even humans working on, or visiting, the farm. The first and the second routes are regarded as the most important ones." (EFSA, 2010).”
To estimate Salmonella risk to consumers via the pork production chain, including feed production, the researchers relied on a quantitative risk assessment model.
The model combined two approaches. “A bottom-up approach was used to estimate the Salmonella risk to pigs from feed ingredients and feeds. Top-down approaches, which started from subtyping data, were used to estimate the relative proportions of pig infections due to feed or the environment and also to estimate the relative proportion of human salmonellosis cases attributable to pork.”
The information and data needed for the risk assessment were gathered from several sources, they said. Sources used included the scientific literature and statistics, Evira reports, data from the customs office, the Finnish Farm Registry and Finnish National Infectious Diseases Register.
“More specific information on feed production practices in feed mills and on farms was collected by carrying out an inquiry targeted at feed mills producing pig feed, pig farms producing their own feeds and mobile mixers mixing pig feed in Finland.
As the feed legislation (2012/548) requires sampling for Salmonella from only those feeds and feed materials produced to be sold, no sampling data were available from feed components produced and used within the same piggery. Therefore it was assumed that the Salmonella prevalence of the feed ingredients used in piggeries was similar to that of ingredients used at feed mills.”
The authors built in various scenarios in relation to data from the years 2013 and 2014. The first set-up was based on the controls, feedstuffs and feeding practices as they were in 2013 in Finland, the next scenario was based on the prevalence of Salmonella in feed raw materials in other European countries, except for Sweden and Norway, factoring in the lower temperatures used in heat treatment of feed in other countries. Finally, they looked at a set-up whereby only Finnish protein-rich feed materials in pig feed were included.
They said that 5.3% of the 300 to 400 domestic human salmonellosis cases per year, reported to the Finnish National Infectious Diseases Register, 2016, can be attributed to pig feed.
The team concluded: “A decrease in the use of foreign feed raw materials could reduce the number of exotic Salmonella serotypes in feed. However, replacing soy in pig feed recipes with ingredients that can be grown in a cold climate is not presently possible due to [the] higher cost [involved].”
In Finland, feed has been controlled for Salmonella based on legislation for more than 50 years.
Control of imported feed and domestic manufacturing has efficiently limited and prevented the spread of Salmonella from factories to farms in Finland. “The strict liability principle in the animal feed legislation and the indemnity liability have contributed to the willingness of feed mills to develop their operations towards eliminating risks of Salmonella,” found an EFSA report.
Finnish feed operators are obliged to pay compensation for damages caused by Salmonella contaminated feeds, and must inform Evira when it is found in feeds, feed materials or manufacturing processes.
Source: Food Microbiology
Title: Salmonella risk to consumers via pork is related to the Salmonella prevalence in pig feed
Published online ahead of print: https://doi.org/10.1016/j.fm.2017.03.017
Authors: M. Rönnqvist, V. Välttilä, J. Ranta, P. Tuominen
The article was updated on May 2 2017 to include the comments from Maria Rönnqvist, researcher, EVIRA.