Effects of Preservatives and Additives on the Gut Microbiota
The gut is the seat of health in horses, dogs, and humans. Variances in the gut microbiota colonies affect neurotransmitters, the immune system, mood, learning capabilities, and overall wellbeing. Imbalances in microbial diversity can contribute to:
Loss of immune homeostasis
Increased likelihood of intestinal dysbiosis, intestinal permeability, and inflammation
Preservatives and additives
Preservatives and additives can be found in processed feeds and supplements, including those that are pelleted, powdered, or liquid.
While studies on the effects of preservatives and additives in the equine gut have not been widely investigated, research on humans, mice, cows, rats, chickens, and dogs illustrates that the microbiome is certainly impacted by specific preservatives and additives.
Common preservative effects in horse feed and supplements
Benzoic acid and sodium benzoate have been shown to disrupt gut microbiota and induce glucose intolerance in mice. They can negatively affect important beneficial bacteria strains, which are important short-chain fatty acid (SCFAs) producers. In horses, various SCFAs provide energy, strengthen the gut barrier, and support immune function. Butylated hydroxyanisole (BHA) has been shown to alter microbial community structure in vitro, ex vivo, and in vivo. Potassium sorbate has been shown to alter the gut microbiome by reducing beneficial bacteria, such as Lactobacillus and Bifidobacterium. It can increase proinflammatory bacteria, such as Entertococcus faecalis and Proteobacteria.
Common additive effects in horse feed and supplements
Artificial sweeteners (which often includes the above-mentioned sucralose) can alter the balance of bacteria and affect SCFA production. Maltodextrin can alter the diversity and abundance of gut microbiota. A study on mice showed that maltodextrin reduced mucin granule content in the gut, demonstrating destruction of the mucosal barrier. Potassium sorbate studies have reported that it restrained the viability of gut microbiota with an alternation in host immunity. It can also affect SCFA levels. Sulfites (sodium bisulfite and potassium bisulfite) can decrease beneficial bacteria species, specifically L. casei, L. plantarum, and L.rhamnosus. Polysorbate 80 can decrease SCFAs, which are incredibly important metabolites of the microbiome. It can induce intestinal inflammation by thinning the gut mucus layer and altering gut microbiota balance. Parabens (methylparaben and ethylparaben) can decrease the prevalence of Lactobacillus and may be linked to metabolic dysfunction. Calcium propionate can cause disruptions in the gut microbiome. It is currently being studied for its effects on the development and exacerbation of autism spectrum disorder (ASD). Artificial flavorings and coloring agents have been linked to increased gut inflammation, triggered allergies, and behavioral issues in children.
Not all additives and preservatives are problematic to the GI tract
Rosemary extract can support the beneficial bacteria strains Lactobacillus and Firmicutes and can reduce the pathogenic Bacteroidetes and Proteobacteria. Soy lecithin and sunflower lecithin (emulsifiers) can improve gut microbiota diversity and strengthen the mucus barrier in the GI tract. These plant-sourced emulsifiers are a far better choice than synthetic emulsifiers, such as polysorbate 80. D-alpha tocopherol and mixed tocopherols (vitamin E) help prevent fats and oils from oxidizing. Vitamin E is a super antioxidant. Citric acid may promote beneficial bacterial strains such as Lactobacillus and Bifidobacterium. Erythritol is a sweetener that has no known effects on the microbiome. In humans, though, it has been associated with increased risk of heart attack and stroke. Agar is generally regarded as safe. However, one study published in March 2021 examined a range of dietary emulsifiers on human gut microbiota; it found that agar had a non-reversible reduction effect on bacterial density.7 Non-nutritive sweeteners (like Stevia) effects remain unclear, pertaining to research. Animal studies report a decrease in Bifidobacterium and Lactobacillus, an increase in the harmful strains (such as Clostridium difficile and E. coli), and disruptions in SCFA production and gut hormone signaling. Human studies showed milder to no significant changes to the microbiome.
Accumulation of preservatives and additives in the gut
When we start adding up all the feeds and supplements containing undesirable preservatives and additives we give each horse, the sum increases the likelihood of microbial imbalance in the gut.
Some researchers refer to this as chronic exposure.
This imbalance can lead to behavioral issues, changes in attitude, GI tract dysbiosis, immune stress, and poor athletic performance.
Preservatives in topicals affect the skin microbiome
Preservatives in topical products may disrupt the skin’s microbial balance. This is due to the residual activity of preservatives on the skin, remaining active after application. Preservatives can interact with the microbes on the skin, changing the balance of the bacterial population. These topicals include soaps, shampoos, and lotions.11
It’s on the label
Many liquid supplements contain at least one preservative.
Some paste supplements contain one or more preservatives and additives.
Commercial feeds generally contain preservatives, as well as additives.
Forage pellets are unlikely to contain preservatives.
Healthy balance of body and mind
Remember: it is the accumulation of less than desirable preservatives and additives in multiple products given to the horse that produces chronic exposure.
If the gut is out of balance, it will affect the GI tract, the mind, and the immune system.
Keep in mind, the microbiome of the skin is affected as well.
Tips on supporting the microbiome in the GI tract
Plant diversity, for the majority of us, is lacking in our pastures. In the US, hedgerows are often not grown like they are in the UK, where horses can pick from a variety of plants along the fence lines. Beneficial bacteria in the gut thrive on various plants and forages. To help with this, add different pelleted forages to the basic alfalfa, orchardgrass, Timothy, and Bermuda hays, like:
Teff Alfalfa oat grass pellets
Quality forage supports the bacteria that ferment fiber to produce the important SCFAs. Some preservatives and additives negatively affect SCFAs.
Learn more about plant diversity in Tigger’s article, From the Outside In: Our Backyard Ecosystems
Fermented foods can increase microbiome diversity. While feeding our horses sauerkraut is definitely not recommended, there are several fermented bagged hays (like Chaffhaye and Alfahay) that can provide benefits to the modulation of the gut-brain axis.
In addition, some herbs are available in a fermented form, such as turmeric and ginger.
Probiotics, like Lactobacillus and Bifidobacterium, are especially sensitive to stomach acids. When giving a probiotic supplement that contains these bacteria, make sure it is either enteric-coated or microencapsulated to ensure the bacteria reach the small and large intestine.
Soil-based organisms (SBOs), such as Bacillus, can survive passage through the stomach, as can yeasts. They are very hardy!
Colony-forming units (CFUs) listed on the label tell you how many active/live bacteria or yeasts there are per serving. 100 Billion CFU’s is more potent than 40 million CFUs.
Prebiotics (dietary fibers in grass and plants) are a great for feeding the colony in the gut, acting as a food source for the gut microbes. Providing a variety of plants in the diet ensures your horse gets the necessary prebiotics.
Studies comparing the fecal microbiome of wild horses versus domesticated horses show that wild horses have a much greater diversity of beneficial bacteria in their GI tract than domesticated horses. This is due to the wider variety of plants and grasses the wild horses consume.12
Common prebiotics in feeds and supplements are fructooligosaccharides (FOS) and mannanoligosaccharides (MOS).
Stress management in horses can be challenging, especially if the horses compete or are in stall confinement due to injury or surgery.
Reducing the amount of less desirable preservatives and additives in your horse’s diet can help reduce stress on the GI tract and reduce anxiety in the brain.
Several studies point to increasing omega 3s (flax, chia, fish oils, and camelina oils) during stressful periods can help reduce anxiety.13
Magnesium can help reduce cortisol. Adding a bioavailable form of magnesium, such as pumpkin seeds, almonds, and bananas, can be helpful in reducing stress. Even better, these food sources have another benefit: increasing diversity of the microbiota in the gut.
Read the labels: preservatives and additives are listed on labels under ‘ingredients,’ not under ‘guaranteed analysis.’
The question I always ask myself
Whether it is a food or supplement for myself, the horses, or the dogs, the question I’ve learned to ask is: Will this increase or decrease stress on the GI tract?
What we eat and what we feed is critically important for a healthy microbial balance and gut-brain connection. Eliminating specific preservatives and additives that have negative effects on the gut microbiome can make a huge difference in attitude, performance, immune health, and gut health.
References
1 Systematic evaluation of antimicrobial food preservatives on glucose metabolism and gut microbiota in healthy mice | npj Sci Food: https://doi.org/10.1038/s41538-022-00158-y
2 Dietary preservatives alter the gut microbiota in vitro and in vivo with sex-specific consequences for host metabolic development in a mouse model | ScienceDirect: https://doi.org/10.1016/j.ajcnut.2025.04.010
3 Common food preservative has unexpected effects on the gut microbiome | Biological Sciences Division: https://biologicalsciences.uchicago.edu/news/food-preservatives-gut-microbiome
4 Sulfites inhibit the growth of four species of beneficial gut bacteria at concentrations regarded as safe for food | PLOS One: https://doi.org/10.1371/journal.pone.0186629
5 Food Additives Associated with Gut Microbiota Alterations in Inflammatory Bowel Disease: Friends or Enemies? | MDPI: https://doi.org/10.3390/nu14153049
6 Common dietary emulsifiers promote metabolic disorders and intestinal microbiota dysbiosis in mice | Communications Biology: https://doi.org/10.1038/s42003-024-06224-3
7 Direct impact of commonly used dietary emulsifiers on human gut microbiota | Microbiome: https://doi.org/10.1186/s40168-020-00996-6
8 Food Additives: Emerging Detrimental Roles on Gut Health | The FASEB Journal – Wiley Online Library: https://doi.org/10.1096/fj.202500737R
9 Exploring the Long-Term Effect of Artificial Sweeteners on Metabolic Health | Cureus: https://doi.org/10.7759/cureus.70043
10 Calcium Propionate and Autism: Why Changing Your Diet Might Not Be Enough | Tesseract: https://insights.tessmed.com/calcium-propionate-and-autism-why-changing-your-diet-might-not-be-enough/
11 Effect of commonly used cosmetic preservatives on skin resident microflora dynamics | Scientific Reports: https://doi.org/10.1038/s41598-021-88072-3
12 Gut Microbiome Characteristics in feral and domesticated horses from different geographic locations | Communications Biology: https://doi.org/10.1038/s42003-022-03116-2
13 Efficacy and safety of omega-3 fatty acids supplementation for anxiety symptoms: a systematic review and dose-response meta-analysis of randomized controlled trials | BMC Psychiatry: https://doi.org/10.1186/s12888-024-05881-2 (p. 2)
About the Author: With over 30 years experience in the equine and human supplement industry, Tigger Montague knows nutrition from the synthetic side as well as the whole food side. She started BioStar US in 2006 with formulas she created in her kitchen. Before she started the company, she was an avid rider and competitor with eventing and show jumping, until she got hooked on dressage in the late 1980’s. She has competed on horses she’s owned and trained all the way from training level to Grand Prix.
