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Reviewed by rabbit expert Lucile Moore, PhD.
Much like anything in our world today, there seems to be quite a bit of controversy surrounding the effect of probiotics in rabbits. Companies like Oxbow don't doubt the potential to influence and strengthen the microbiome through probiotics¹ but they argue that there simply isn't enough evidence to support it yet. Other sources like the Textbook of Rabbit Medicine state "Despite theoretical doubts about the efficacy of probiotics in rabbits, there are many anecdotal reports that they are effective".² Even for humans, the scientific community often disagrees on what the benefits of probiotics are, as well as which strains of bacteria are responsible.³ Despite the controversy, many people still swear by them.
I get it! It all feels a little confusing. So let's talk about it!
Probiotics are bacteria and fungi (often yeasts) that help keep the microbiome (aka allllll of the billions of microscopic living organisms that set up shop in the GI tract) of the gut balanced and healthy. Probiotics are the little warriors of the gut, oftentimes referred to as 'live' or 'good' bacteria. They are bio-regulators (a bad-ass title if I do say so myself!) of the intestinal micro-flora and reinforce the host’s natural defenses⁴, promoting immune, digestive, brain, & heart health among other benefits. Amazing work for such little things!
In Rabbit Nutrition and Nutritional Healing, Lucile Moore highlights two unique values of probiotics for rabbits that are not commonly discussed:
Lactobacillus acidophilus has been found by researchers to reduce the amount of blood urea and cecal urea in rabbits as well as excreted ammonia. This use of probiotics could be of particular value where multiple rabbits are housed in close proximity. As noted in Chapter 7, lactobacilli may have another positive benefit for rabbits because the bacteria “eat” oxalates, phytochemicals that can affect the absorption of calcium and magnesium.⁹
Rabbits are hind-gut fermenters meaning they have a special sack in their GI tract called the cecum. The cecum is a unique pouch located where the small and large intestines connect and makes up a whopping 40% of the total GI system in rabbits! In the cecum, rabbits use massive quantities of bacteria to convert indigestible fibre to digestible nutrients.⁵
The cecum is pretty amazing - I like to think of it as rabbit's very own little supplement factory! It forms cecotropes which are ingested straight from the anus and contain an abundance of essential vitamins, nutrients, and fatty acids (sources of energy). They're like superfood poops! Super-poops! Cecotropes are important to rabbits' health so we want the cecum to be happy and healthy.
Rabbits are particularly sensitive to dysbiosis (imbalance between ‘good’ and ‘bad’ gut bacteria) so helping them maintain a healthy balance is key. In fact, a published article from The Journal of Applied Microbiology states:
The high incidence of gastrointestinal diseases in rabbits is often related to abnormalities in the composition of bacteria. Any imbalance of microflora can lead to pH alteration, dysbiosis and pathogens proliferation, with adverse effects on animal health. The establishment of a healthy, stable and diverse microflora in gastrointestinal tract is of great significance for rabbits to resist intestinal diseases.⁵
Simply put, if the bacteria in the gut aren't balanced and happy, your rabbit has a much higher chance of getting sick with some variation of GIT (gastrointestinal tract) disease.
Hopefully we've successfully highlighted how important it is to keep the delicate microbiome of the gut happy and balanced. You can see why it might be easy to come to the conclusion of "okay I get it, so my rabbit needs to maintain happy, healthy bacteria levels in the gut to avoid health problems, so why don't I just give her probiotics as a preventative measure?"
Not so fast, folks! First and foremost your rabbit must be consuming a proper, well-rounded diet to support a healthy gut. Providing your rabbit with a low-stress environment, exercise, and consistent proper grooming will also help maintain your rabbit's health and work as preventative care in and of itself. In our research, we found that if your rabbit is healthy, they likely do not need to be supplemented with probiotics. While preventative probiotic intake does not seem like it will hurt, maintaining gut balance should and can be achieved primarily through proper diet and environment.
Sometimes proper diet isn't enough and issues like surgery, illness/disorders (like pain or other underlying health conditions), antibiotics, and even stress can throw off the microbiome's balance and this is when a little probiotic/prebiotic supplementation could be beneficial.
Prebiotics in simplest of terms are the fertilizer for probiotics. They are usually types of fiber naturally found in vegetables, fruits, and legumes and are not digested in rabbits until they reach the cecum and large intestine where probiotics then digest them⁸ which promotes the growth of more beneficial bacteria.
Yucca schidigera is a very common prebiotic used in pelleted food and treats for rabbits. We previously mentioned the probiotic Lactobacillus acidophilus reducing ammonia levels; in one study yucca was actually found to be more effective at reducing urea and ammonia levels than Lactobacillus acidophilus. Yucca is also a powerful antioxidant and may boost the immune system and act as an anti-inflammatory agent. Chicory root (inulin) and brewer's yeast are other common prebiotics used. Oats and banana (two common ingredients in our products) are also great sources of prebiotics!
There do not seem to be any negative side effects reported regarding offering adult rabbits probiotics, however some sources still caution "that because of the rabbit’s unique and sensitive digestive system, it cannot be assumed that a probiotic or prebiotic that has been tested in other species will necessarily be safe or effective for rabbits".⁹
In one study from 2019 observing the effects of probiotics on 4 week old rabbits (specifically Lactobacillus Plantarium which is an example of a strain not naturally found in the rabbits' system), the researchers stated that
...it can be concluded that probiotic (Lactobacillus Plantarium) at the tested levels can be applied in rabbit rations to improve the productive and physiological performance, as well as gut health.⁷
Therefore, at least in young rabbits, it seems as though probiotics that don't naturally exist in their system may still have benefits when supplemented to the diet.
Caution would be advised when considering giving probiotics to immunosuppressed rabbits* as some introduced microbes have the potential to become pathogenic under the right conditions. It is possible that probiotics can cause infection in severely immunosuppressed humans, and probably in severely stressed or immunosuppressed rabbits as well.⁹
There's no doubt that probiotics have beneficial effects on rabbit health in a variety of ways and many vets will now even recommend their use in certain cases. It's worth noting that many of the studies done thus far have been on young rabbits so it's a little difficult at this point in time to determine if the positive effects are the same in adult rabbits, although there is bountiful anecdotal evidence suggesting so.
Because there is no reported harm and no known side effects in rabbits (and because there have been some studies showing positive effects), we recommend utilizing probiotics
It is suggested that probiotics are not a "one and done" fix and must build up in the system¹ so it is recommended to start using them at least 5-7 days before a known stressful event.
An alternative solution to probiotics recommended by some vets and rabbit experts is to offer cecotropes from another healthy rabbit to the sick rabbit. Some cautions with this method include:
Prebiotics are lauded because they are not species-specific, they feed the good bacteria already in the gut, and they can be added to the diet safely without introducing new bacteria to the GI tract.
We suggest using PRObiotics for digestive disorders, after surgery, while on antibiotics, or preventatively in extreme stressful situations but do not find them necessary as an everyday dietary additive for healthy rabbits (although we also don't believe they will cause harm if they are used this way). PREbiotics are safe to add to the diet via treats or pelleted foods and are a great natural way to boost the good bacteria already in the gut.