Feedstuffs are the basis for the production of safe foodstuffs of animal origin. Despite the low water activity (aw), however, compound feed can always be contaminated with pathogenic germs. The highest risk for contamination of feed is from Salmonella spp. Special components, such as meal from oil seeds and protein feed of animal origin are considered as high-risk feed.
More than 80% of Salmonella reports in the European Rapid Alert System for Food and Feed (RASFF) can be traced back to these components. Besides Salmonella spp. the contamination with other pathogens such asClostridium perfringensorListeria monocytogenesare also found in compound feed. These organisms can survive long periods in feed, due to the nutrients and moist content of the feed. When contaminated feed is consumed, pathogenic microorganisms can be transferred to the animals, which is documented as Salmonella in different studies for different animal species.
When infected animals are slaughtered and further processed, the pathogens can enter the human food chain and thus initiate an infection chain from animals to humans.The legal framework established by the EU (EC regulation on control of Salmonella and other zoonotic agents) and the feed hygiene regulation give feed producers the responsibility for the safety of feed. It clearly states that contaminated feedstuffs must be withdrawn from the market and that the costs of eliminating feedstuffs must be borne by the manufacturer. However, if an effective decontamination of the feed can be demonstrated, further processing is possible. On 13 December 2016, the FEFAC workshop “Salmonella Risk Management in Feed” took place in Paris, where the importance of feed hygiene was once again addressed. Recent research, among others at the AGES in Austria, also reveal the need for more work into this topic.
Do organic acids control Salmonella?
Salmonellais the main zoonotic agent transmitted fromcontaminated porkto humans.That is why its control is addressed as afood safety issue.On-farm control success is limited by the complex epidemiology and the lack of any particular effective interventions. Organic acids are popular among on-farm alternatives to control Salmonella. Their efficacy is affected by factors such as the acid and the concentration chosen or the duration of the treatment.
On-farm control of Salmonella can include different strategies. The use of organic acids, either in feed or water, is one of the most popular. Short-chain (for instance, butyric or propionic) and middle-chain (caproic or caprilic) organic acids and other organic acids such as lactic or formic acid are able to improve gut health by their antibacterial activity against pathogens such as Salmonella. They also improve the conditions for beneficial microbiota (lactic-acid bacteria), which competes directly for the intestinal niche with the pathogen.
Factors that affect the efficacy of organic acids against Salmonella:
Acid used: Not all the acids have the same effect. Research studies highlight that butyric, propionic or formic acid effectively reduce Salmonella levels while the same or other studies point out that other acids, principally acetic acid, have no beneficial effect against Salmonella.
Presentation: Commercial products usually encapsulate the acid or mix of acids included in the formulation. Some of these products also include other compounds, such as essential oils, other antimicrobials, etc. The inclusion of these compounds and the encapsulation may boost the effect of the product.
Concentration: Concentration used is one of the key factors. The higher the concentration, the better the results. For instance, a study combining formic-propionic acids was effective reducing Salmonella shedding in feed when the product was used at 1.2 percent, but not when it was administered at 0.8 percent. The limitation of using higher concentrations is that cost is increased and the intervention could not be feasible from an economic point of view.
Treatment duration: Treatment duration is the other key factor. The right combination duration-concentration will determine the success or failure of the intervention. In general, short treatment periods (between 2 weeks and 4 weeks) have yielded poor results. Studies using propionic, formic, butyric or a mix of acids at a concentration between 0.3 percent and 2 percent for prolonged periods (between 6 and 12 weeks) could decrease the percentage of pigs shedding Salmonella in feces.
Salmonella serotype: In contrast to vaccines, the effect of organic acids is not serotype-dependent.
Cost-benefit analysis of use of organic acids
First of all, it must be noted that despite the infection in most of occasions subclinical, there is a lower performance of infected pigs compared to Salmonella-free pigs. For instance, in a study in grower pigs, feed conversion efficiency (Kg/Kg) (FCE) was 1.88 and 1.66 in Salmonella-infected and Salmonella-free animals, respectively. Cost-benefit analysis in different commercial products revealed interesting data. Using these products at the recommended rates, FCE was improved in pigs with the acid diet compared to the control diet, together with a better cost of feed per Kg of live weight gain (EUR0.89 in the control feed and EUR0.84 in the feed supplemented with the acid).
Organic acids as a strategy
Organic acids are one of the strategies offered to control and reduce Salmonella levels on the farm. The market offers lots of products with different combinations of organic acids. The right dose and treatment duration are essential for success, but acids need other on-farm interventions related to hygiene, biosecurity and management to reduce Salmonella to negligible levels.
A combination of hydrothermal treatment and the use of organic acids can successfully de-contaminate feed. This was shown by research from the German Research Institute of Feed Technology.
At the IFF Research Institute of Feed Technology, a multi-stage industry research project for hygienisation is being carried out using a combination of hydrothermal treatment and various organic acid preparations. A total of 15 project partners in the field of feed production, plant construction, additive production as well as an association of value chain in Germany have decided together with the IFF Research Institute to continue the research in this area. The fact that additional financial support from the Victam Foundation was granted once again points out the importance of hygienisation in the feed industry, not only in Germany.
In the first project section, the treatment of two mash compound feeds (broiler feed and laying hen feed) and a single feedstuff (rapeseed meal) are carried out in order to assess different buffer effects (between 740 and 2,150 mEq/kg) on the efficacy of the treatment. Since the Research Institute is not allowed to infect Salmonella-free feedstuff artificially with Salmonella or work with naturally Salmonella-contaminated feedstuffs, the individual feedstuffs are inoculated with a suitable a-pathogenic test germ from the family of Enterobacteriaceae (Escherichia coliDSM 498).
在第一个项目部分，为了评估不同缓冲效应（740和2150 mEq/kg之间）的处理效果，对两种混合饲料（肉鸡饲料和产蛋鸡饲料）和单一饲料（菜籽粉）进行处理。由于研究所不允许用沙门氏菌人工感染无沙门氏菌的饲料或使用自然条件下受到沙门氏菌污染的饲料，所以从肠杆菌科（大肠杆菌DSM 498）中选择合适的致病菌来接种饲料。
This test organism according to current knowledge has a similar degradation behaviour as pathogenic Salmonella in hydrothermal and/or chemical stress. The contaminated batches are treated hydrothermically at different treatment temperatures or with additional use of 85% formic acid or one of three acid preparations, which are added during the conditioning. The acid preparations are two liquid products and a powdered product, which are made available by the manufacturers and are used in dosage rates between 0.1 and 2.5% as required by the project partners. The effectiveness of the treatment is microbiologically examined at defined times between one day and 12 weeks.
The results obtained so far suggest that a combined approach of hydrothermic/mechanical treatment and the simultaneous use of organic acid preparations during conditioning (de-pending on their dosage) brings various advantages compared to a solely hydrothermical mechanical treatment. Depending on the dosage of the acid preparations, the liquid products show, as expected, a markedly better effect than the acid adsorbate on direct comparison, with which the same results are achieved in some cases only after a considerably extended exposure time.
Even after cooling/drying the treated feed, a contamination of the feed seems to be prevented by the use of organic acid preparations during the hydrothermal treatment, which could make an additional preservation of the feed unnecessary. An in-depth implementation and further development of the obtained findings will be taken up in a follow-up project after completion of the current research project.