Organic acids: How the mode of action delivers benefits | INFOGRAPHIC
Download this comprehensive A3 infographic to understand how organic acids can benefit your operation. For further questions or feedback, we’ll be happy to hear from you.
Download this comprehensive A3 infographic to understand how organic acids can benefit your operation. For further questions or feedback, we’ll be happy to hear from you.
feedby Dr. Inge Heinzl, EW Nutrition
Salmonella infection in poultry is a problem for the producer because of the performance losses of his flock. At the same time, products of salmonella-contaminated animals pose a severe risk to human health. In the USA, Salmonellosis in poultry is estimated to cost $ 11.6 billion each year (Wernicki et al., 2017) and more than € 3 billion in the EU (Ehuwa, 2021). As the use of antibiotics needs to be reduced to keep them effective, Salmonella control in poultry requires new solutions. This article shows how organic acids and phytomolecules can help to fight this problematic disease.
Salmonellosis is a zoonosis, meaning that it can be easily transferred from animals to humans. The transfer can occur via different routes:
Frozen or raw chicken products, as well as the eggs of backyard hens, are the most frequent causes of animal-mediated Salmonella infections in humans. The following graphic shows a clear relationship between the occurrence of Salmonella in layer flocks and the event of disease in humans:
Within the poultry flock, there are two ways of spreading: the fecal-oral way (horizontal infection) or the infection of the progeny in the egg (vertical infection). The effects of the disease depend on the age of the birds: the younger the animals, the more severe the impact.
If the brood eggs already carry salmonellae, the hatchability dwindles. During their first month of life, infected chicks show ruffled downs and higher temperatures. Diarrhea leads to fluid losses and frequently to the chicks’ death.
Adult animals usually do not die from Salmonellosis; often, the infection remains unnoticed. During a substantial acute salmonella outbreak, the animals show weakness and diarrhea. They lose weight, resulting in decreased egg production in layers and worse growth performance in broilers. The birds need more water to compensate for the fluid losses, and their crowns and jowls appear pale.
Salmonellae have developed a clever way to protect themselves. After they arrive in the gut, they attach to the epithelial cells and form small molecular “syringes” to inject divers substances into the gut cells (Type-3-injection system). These signaling substances make the gut cells bulge their membranes and enclose the bacterium. Finally, the manipulated gut cell absorbs the Salmonella, the host “allows” the bacterium to enter, and it can proliferate in the gut cells (Fischer, 2018).
When an antibiotic is attacking the bacterium, Salmonellae stop their cell division. Since many antibiotics are only effective against bacteria during cell division and growth, Salmonellae survive the attack by staying as dormant variants or persisters until the treatment stops (Fischer, 2018).
The genus of Salmonella consists of more than 2600 serovars (Ranieri et al., 2015), of which less than 100 are relevant for humans (CDC, 2020). More than 1500 serovars belong to the Salmonella enterica subspecies that colonize the intestinal tract of warm-blooded animals. These serovars are responsible for 99 % of salmonella infections (Mendes Maciel et al., 2017). The main serovars relevant for poultry are S. Gallinarum and S. Pullorum, but also S. Enteritidis, Typhimurium, and in recent years, S. Kentucky, S. Heidelberg, S. Livingstone, and S. Mbandaka (Guillén et al., 2020).
Several Salmonella serovars are critical for animals and humans. Since more than 91,000 salmonellosis cases are reported for Europe and more than 1.35 million for the USA every year (EFSA, 2022; FDA, 2020), their spread must be prevented by all means. Governments have enacted some laws to curtail this disease. The EU, for example, implemented extended control programs for zoonotic diseases, with Salmonella set as a priority. These programs include the provision of scientific advice, targets for reducing Salmonella in poultry flocks, and restrictions on the trade of products from infected flocks.
For farmers and vets, this means the obligation to notify the occurrence of the disease to the authorities. Depending on the country, it also entails compulsory vaccination and the documentation of hygienic measures. In the EU, due to the risk of developing resistances, the EFSA recommends limiting the use of antimicrobials to individual cases, e.g., to prevent inordinate suffering of animals.
The best strategy for salmonella control is prevention based on three key points (Visscher, 2014):
For this purpose, the following steps are requested/recommended:
The use of well-absorptive material such as wood shavings, straw pellets, or straw granulates and regular removal of the used litter is recommended. The animals must be controlled for diarrhea to avoid wet droppings. The water supply must be adequate; an excessive water supply wets the litter.
To keep the poultry house clean, broken eggs and dead animals (potential sources of infection) must be removed. In general, the houses should be cleaned and disinfected before every restocking.
Clean feed and water are essential; therefore, feed should not be stored outside but be kept dry and protected from pests and rodents. The feeding of the animals should take place inside to avoid contamination by wild birds. Concerning the water for drinking, the flow rate must be high enough to provide the birds with sufficient water but not too high that the floor gets wet. The troughs must be clean from droppings.
To limit the spread of Salmonella, only a restricted number of persons can have access to the flocks. They must wear clothes, and instruments should be exclusively used for the respective poultry house.
Salmonellae are a genus in the family of Enterobacteriaceae. They are gram-negative, rod-shaped (size: approx. 2 µm), glucose-fermenting facultative anaerobes that are motile due to peritrichous flagella. Since Salmonellae do not form spores, they can be easily destroyed by heating them to 60°C for 15-20 min (Forsythe, 2001), especially in food/feed with higher water content.
For the storage of food, Bell and Kyriakis (2002) found that most serovars of Salmonella will not grow at temperatures lower than 7°C and a pH lower than 4.5. Wessels et al. (2021) showed optimal growth conditions for Salmonella: temperatures between 5 and 46°C (optimum 38°C), a water activity of 0.94-0.99, and a pH of 3.8-9.5.
A high fat content in the feed or food increases the likelihood of infection with Salmonella because the fat protects the bacteria during the passage through the stomach. Doses of 10 to 100 Salmonella cells can already pose a severe risk (University of Georgia, 2015).
To reduce the incidence of Salmonella while simultaneously lowering the use of antibiotics in animal production, there are different possibilities. On the one hand, veterinary medicine offers vaccines. On the other hand, the feed industry provides additives that strengthen the immune system, improve gut health, or support the animals in another manner. Other than pro- and prebiotics, the main active ingredient categories for such additives are organic acids and phytomolecules.
Already in ancient Egypt, the method of fermentation and the generated acids have been used for the conservation of food (Ohmomo et al., 2002). Nowadays, it is a standard tool to protect feed (silage) and food from spoilage. Also for animals, organic acids added to the feed or the water have proven helpful against pathogens. These modes of action can be combined against Salmonella: reducing the pathogen load in the feed to limit the intake of bacteria and fighting against these pathogens in the animal.
In general, the antimicrobial activity of organic acids in feed is based on lowering the pH (Pearlin et al., 2019). pH-sensitive bacteria such as Salmonella minimize their proliferation at a pH <5. Additionally, the organic acids attack bacteria directly. The acid’s undissociated and more lipophilic form penetrates the bacterial cell membrane. At the neutral pH within the cell, the acid dissociates, releases protons, and lowers the pH, leading to the impediment of metabolic processes in the cell. The cell spends a lot of energy trying to get the pH back to neutral (Mroz et al., 2006). Additionally, the anions become toxic for the cell metabolites and disrupt the membrane (Russel, 1992).
According to Hernández and co-workers (2006) and Thompson and Hinton (1997), the addition of organic acids to the feed does not change the pH in the various digestive tract segments. Still, literature shows a clear reduction of Salmonella in the gut or litter when using propionic or/and formic acid (McHan and Emmett, 1992; Hinton and Linton, 1988; Humphrey & Lanning, 1988). A likely mode of action is described by Van Immerseel et al. (2004). He asserts that SCFAs such as propionic and formic acid as well as MCFAs can inhibit Salmonella’s penetration of the intestinal epithelium and, therefore, can control these invasive phenotypes of Salmonella (S. Typhimurium and S. Enteritidis).
Depending on the acid, the efficacy against Salmonella varies (see figure 3). Formic acid shows the highest effect, followed by fumaric acid. Then, lactic, butyric, and citric acid follow, showing lower efficacy.
An in-vitro trial was conducted at a commercial research facility in the US to test the efficacy of Acidomix AFL, a liquid mixture of propionic and formic acid, against Salmonella. The bacterial strain used in these studies was nalidixic acid-resistant Salmonella typhimurium. The bacteria were maintained in broth cultures of tryptic soy broth.
They were added to 5 g of dry feed in a 50 ml tube to a final concentration of 40,000 CFU/g. Next, Acidomix AFL was added to the desired inclusion rate, and the samples were incubated at room temperature. After 18 to 72 hours of incubation, viable bacteria were counted using the plate count method.
Results: As shown in figure 4, the trial found that at an inclusion rate of 2.0 %, Salmonella inhibition was nearly 100 %. Already at a 0.4 % inclusion rate, Salmonella could be reduced by 45-60 %, showing a clear dose dependency.
Plants produce phytogenic substances to protect themselves from molds, yeasts, and bacteria, among others. After several purification steps, these phytomolecules can be used to fight Salmonella in poultry. They work through different modes of action, from attacking the cell wall (terpenoids and phenols) to influencing the genetic material of the pathogenic cells or changing the whole morphology of the cell.
Due to the different modes of action, it was long thought that there would be no resistance development. Still, Khan et al. (2009) found some microorganisms such as multidrug-resistant E. coli, Klebsiella pneumoniae, S. aureus, Enterococcus faecalis, Pseudomonas aeruginosa, and Salmonella typhimurium can show a certain – perhaps natural – resistance to some components of herbal medicines.
Gram-negative bacteria such as Salmonella are usually less attackable by phytomolecules because the cell wall only allows small hydrophilic solutes to pass; however, phytomolecules are hydrophobic. However, mixing the phytomolecules with an emulsifier facilitates the invasion into the cell. Their efficacy depends on their chemical composition. It is also decisive if single substances or blends (possible positive or negative synergies) are used.
The best-clarified mode of action is the one of thymol and carvacrol, the major components of the oils of thyme and oregano. They can get into the bacterial membrane and disrupt its integrity. The permeability of the cell membrane for ions and other small molecules such as ATP increases, decreasing the electrochemical gradient above the cell membrane and the loss of energy equivalents.
Two different phytogenic compositions were tested for their efficacy against Salmonella.
To evaluate its potential as a tool for antibiotic reduction, a trial was conducted to test the antimicrobial properties of Activo Liquid, a mixture of selected phytomolecules and an organic acid designed for application in water. The laboratory test was carried out at the Veterinary Diagnosis Department of Kasetsart University in Thailand. Standardized suspensions [1×104 CFU/ml] of three poultry-relevant Salmonella strains were incubated in LB medium, either without or with Activo Liquid. The tests were run at concentrations of 0.05%; 0.1%; 0.2% and 0.4%. After incubation at 37°C for 6-7 hours, serial dilutions of the cell suspensions were transferred onto LB agar plates and incubated for 18-22h at 37°C. Subsequently, colonies (CFU/ml) were determined.
Results: Activo Liquid was found to be growth-inhibiting to all Salmonella strains from a concentration of 0.1% onwards. At 0.2%, Activo Liquid already exhibited bactericidal efficacy against all tested Salmonella isolates, which was confirmed at a concentration of 0.4%.
On Mueller Hinton agar plates where Salmonella enterica were spread uniformly, small disks containing 0 (control, only methanol), 1, 5, and 10 µl of Ventar D were placed and incubated at 37 °C for 16 hours. The presence of clearing zones indicates antimicrobial activity.
Additionally, a motility test was performed in tubes with a motility test medium containing 0 (control) and 750 µL Ventar D. For this purpose, one colony of Salmonella enterica grown on the agar was stuck in the middle of the medium and incubated at 37 °C for 12-16 hours. Growth can be visualized through the formation of red color.
Result: Ventar D inhibited S. enterica in a dose-dependent manner. Clearing zones were visible within the lowest tested concentration. At its inhibitory concentration, Ventar D suppressed S. enterica motility (figures 5 and 6).
The zoonosis Salmonella generates high costs in the poultry industry. As Salmonellosis can be transferred to humans, it must be kept under control by all means. Antibiotics are one tool to fight Salmonella, but they have their “side effects”: they are no longer well respected by the consumer, and, even more critically, they create resistance. To help keep antibiotics effective, poultry producers seek to use effective but not resistance-creating natural solutions against Salmonella.
As shown with the reviewed trials, organic acids and phytomolecules are highly active against diverse Salmonella serovars. Accordingly, feed additives based on these active ingredients offer effective tools for controlling Salmonella in poultry while also contributing to the overarching aim of reducing antibiotic use in poultry production.
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by Daniela Vega Sampedro, Product Manager Organic Acids, EW Nutrition
Feed spoilage is a significant issue for the feed industry, leading to loss of nutrients, feed waste, and substantial economic issues for feed and animal producers worldwide (Leyva Salas et al., 2017). Fungal growth is one of the main causes of feed spoilage; it can occur at any stage of the feed production chain, including grain pre- and post-harvest processes, during feed production or storage. Organic acids and their salts are globally used in animal nutrition for microbial preservation and supporting animal health.
Organic acids help preserve animal feed and prevent spoilage through molds, yeasts, and mycotoxins
Yeasts and molds can have both positive and negative effects on products consumed by animals and humans. On the one hand, yeasts are used to produce fermented products, such as bread, wine, and beer. On the other hand, yeasts and molds promote the spoilage of raw materials, food, and feeds (Lowes et al., 2000). Molds are among the most potent food and feed spoilers. They can be very resilient to environmental stress, which is a concern in climate change scenarios (Perrone et al., 2020) and enables them to withstand feed preservation measures (Punt et al., 2020).
Several hundred species of molds and yeasts can invade a large variety of raw materials and feeds. They show an easy adaptation to different environments; for instance, they can grow and reproduce in media with pH levels ranging from 2 to above 9 (Tournas et al., 2001). However, the majority of yeasts and molds require free oxygen to grow and thrive.
Excess moisture, high water activity, and high temperatures in feedstuffs are the main mold growth factors that concern the feed industry (Mohapatra et al., 2017). At storage, grains’ moisture content should not exceed 13%, and the water activity of raw materials, feedstuffs, and finished feed should be maintained below 0.8 (Dijksterhuis et al., 2019). Controlling these points contributes to preventing the growth of most pathogens and undesirable microorganisms.
Mold growth reduces the nutritional value of feed, which affects animal health and performance
The microbial growth dynamic of grain storage depends on several factors, including the harvest season, grain temperature and moisture content, as well as the type of facility and its environment. For instance, in some areas, grains are harvested at the beginning of the cold season and stored through the following warm season. Storage molds constitute a significant threat to the quality of these raw materials, especially during the warm months, when the stored grains may become hotter than the surrounding environment. This leads to condensation, which increases moisture and water activity. Molds easily thrive in these conditions.
Storage molds reduce the nutritional and commercial value of grains and feeds. For grains, their commercial value decreases when the appearance of kernels changes in a manner recognized by the grain industry as kernel damage. The chemical composition of feeds may deteriorate due to enzymatic actions, resulting in a loss of nutrients (energy, vitamins) and the production of free fatty acids and other unwanted by-products (Reed et al., 2007).
Extensive research has established the factors that influence mold-induced deterioration during grain storage and which management strategies are required:
The consequences of storage deterioration include:
Beyond their negative impact on feed quality, some fungal genera such as Aspergillus, Penicillium, Alternaria, and Fusarium can produce mycotoxins, secondary metabolites that have toxic effects on humans and animals (Greco et al., 2015). Roughly 60% of raw materials produced for agriculture purposes worldwide are estimated to be contaminated by fungi and mycotoxins (Eskola et al., 2020). Mycotoxins can induce toxic, carcinogenic, and mutagenic reactions even at low concentrations. Their presence in the final feed is a sign of alert as, usually, these metabolites are resistant to technological treatments. Thus, it is important to stop them from entering the feed production chain (Leyva Salas et al., 2017).
Feed-contaminating Fusarium species produce mycotoxins such as trichothecenes, zearalenone, and Fumonisin.
It is crucial to reduce the feed losses and improve animal health by controlling fungal contamination at all stages of the feed production chain: from pre-harvest strategies on the field to post-harvest management during storage and even at feed processing. Throughout these processes, producers can apply different management practices. For instance, in field crops, fungal growth can be prevented through crop rotation and tillage; the use of fungicides is a later measure when mold presence exceeds critical levels.
Post-harvest management of grains and their by-products includes drying and storage management through moisture and temperature monitoring and aeration programs. Other spoilage-prevention measures include good hygiene practices and thermal treatments in feed production. However, feed producers and farmers face limitations in applying and linking such measures to tackle the occurrence of these undesirable pathogens (Dijksterhuis et al., 2019).
Certain organic acids, such as propionic, sorbic, benzoic, and acetic acids, have proven effective in preventing mold growth and feed spoilage. These organic acids are used globally now, not only for improving animal nutrition but also for supporting animal health (Dijksterhuis et al., 2019).
Pro-Stabil BSL is a product that harnesses the feed preservation effects of organic acids and combines them with surfactants. This means that it can offer a strong yeast and mold inhibition while maintaining the moisture in feed, thus reducing the risk of microbial challenges while prolonging the shelf life of feedstuffs and compound feeds.
Pro-Stabil BSL contains a synergistic blend of organic acids and a surfactant that leads to
» Improved moisture dispersion in the feed
» Increased water retention (reduced water activity)
» Improved anti-mold agent dispersion in the feed and grain
Trial results show a significant decrease in mold growth when Prostabil BSL was added to compound feed. In addition, when moisture was added at 2%, moisture from the environment was also observed, but the mold counts still decreased (Figure 1).
Figure 1: Effects of Pro-Stabil BSL with addition of 2 % moisture on feed quality indicators
When adding Pro-Stabil BSL to animal feed, the following benefits can be expected:
Mold growth can lead to sensory defects in feed and reduce its nutritional value. It can also harm animals through the production of mycotoxins. Pro-Stabil BSL offers a safe solution that is also easy to handle. Using the preservative properties of organic acids, Pro-Stabil BSL helps to reduce feed spoilage and its associated effects on animal health and performance.
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by Vinil Samraj Padmini, Global Category Manager, EW Nutrition
Feed safety is essential for animal health and performance – and food safety. Inadequate feed sanitization is still a problem across the globe. It impacts not only the feed industry and animal producers but also puts workers and consumers at risk of being exposed to harmful substances.
Developing a hygiene program for the whole feed chain needs to include proper monitoring of microbial growth, as well as feed processing methods that prevent feed contamination and enable decontamination. This article outlines the importance of feed hygiene and focuses on how organic acids help reduce contamination from “farm to fork”.
Corn is often contaminated with Aspergillus fungi that can produce poisonous mycotoxins
Feed hygiene requires the control of microorganisms throughout the feed production chain. However, producers or retailers can rarely certify or verify feedstuffs’ safety due to the wide range of potential microbial contamination agents and hazards encountered in different feed environments (den Hartog, 2003). The relationship between feed and microorganisms varies, depending on the conditions: feed can transport pathogenic microorganisms and thus directly transmit disease; likewise, microorganisms can also be responsible for feed spoilage and thereby indirectly cause issues (Baer, Miller, and Dilger, 2013).
Since its foundation, the World Organization for Animal Health (OIE) has established standards, guidelines, and recommendations for toxin risk management, including for microorganisms that are transmissible via feed. Recurring outbreaks of Salmonella, Escherichia coli, and other familiar Enterobacteriaceae are a key concern for animal health professionals and the feed industry (Elsayed et al., 2021). However, as factors ranging from climate change to genetic mutations come into play, feed producers are working with moving targets; some of the most significant issues they might face tomorrow are unknown today. There are no easy solutions to these multifactorial problems – but in any case, corrective measures need to include quality control and quality assurance for assessing and managing the pathogenic and microbial risk situation.
To improve animal productivity sustainably, producers regularly experiment with modifying production techniques, innovating feed formulations, but also exploring new ingredients. The inclusion of new ingredients such as animal proteins, oils, and fermented products, among others, heightens the need for strict feed quality monitoring (Truelock et al., 2020). New ingredients come with causative agents of feedborne illnesses, some of which might be unknown (Goodarzi Boroojeni et al., 2016). Therefore, feed and animal producers need to consider how feed changes impact feed safety and include these hazards in their planning and risk assessments.
For any animal production, feed processing constitutes the most crucial part of feed hygiene management, as it covers all treatments of the feed before ingestion. It is referred to as “hydrothermal processing” due to the use of heat that is required to kill most of the pathogens in raw materials, feedstuffs, and compound feed (Jones, 2011). However, whether or not hydrothermal processing will effectively eliminate a given pathogen depends on its heat resistance. Moreover, factors such as the type of feed components involved and water activity levels also need to be considered to reduce microbial pressure (Doyle and Mazzotta, 2000).
The new generation of feed milling equipment – besides elevating feed costs – can also improve feed quality (Truelock et al., 2020). These technologies tend to enhance feed stability and hygiene by modifying the physicochemical properties of the ingredients. This improves the absorption of nutrients, thereby enabling a higher feed intake efficiency with positive results for animal performance (Abdollahi, Svihus, and Ravindran, 2013). However, while increasing processing time at a given temperature can lead to a better decontamination process, it can also negatively affect some nutrients’ dynamics. This includes enzymes, proteins, minerals, vitamins, fiber and starch, and especially non-starch polysaccharides (Goodarzi Boroojeni et al., 2014).
Hence, while significant progress in feed science and feed production technology has already been made, researchers and the industry are still searching for alternative approaches to supporting feed hygiene (Goodarzi Boroojeni et al., 2016). Organic acids are a central research field as they offer promising antimicrobial properties. In combination with feed mill techniques, they already play an essential role in feed preservation (Brul et al., 2002). Despite their efficacy in inhibiting microbial growth, weak organic acids are safe to handle (especially when they are buffered) compared to inorganic acids.
In addition to their preservative effect in feed, it has been shown that organic acids can support gut health. They are not just antimicrobial agents but also acidifiers that display their impact in the stomachs of monogastric animals (Tugnoli et al., 2020).
To support the feed industry and animal production in light of feed safety challenges in AGP-free production, EW Nutrition focuses research efforts on maximizing the beneficial effect of organic acids. The ACIDOMIX® range of products supports the stabilization of the gastrointestinal microflora, inhibiting pathogenic bacterial growth in feed and water. Acidomix is an efficient acidifier specially formulated to have strong antimicrobial effects applicable in feed hygiene programs. Various powder and liquid solutions offer a wide range of benefits:
Feedstuffs and compound feed are at risk of contamination and re-contamination throughout the feed production chain: processing, transportation, delivery, storage, and on-farm. Thus, a holistic and integrated approach that includes optimized feed mill processing and customized organic acids is required to improve the feed’s hygiene status. The positive effects are clear: feed producers benefit economically, animal producers reap the effects of improved animal health and performance, and people get to enjoy producing and consuming safe and nutritious food.
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