by Nadene Stapleton, Veterinary Surgeon This article was published in Rabbiting On Spring 2019
Anyone who takes the time to get to know rabbits can attest to the fact that they have personalities as unique and individual as our own.
It might, however, surprise you to learn that each rabbit’s digestive system has its own individual quirks and personalities as well.
Complex digestive system
Rabbits have a very specialised and complex gastrointestinal tract or ‘gut’. Arguably the most important element of the gut is the big fermentative vat called the caecum. This is where distinctive faeces called ‘caecotrophs’ or ‘night faeces’ are formed.
The caecum or ‘hind gut’ is where a diverse population of bacterial species live. This bacterial population, called the microflora of the gut, help the rabbit extract nutrients from the food they eat. This process, called microbial digestion, also produces important vitamins that the rabbit cannot get elsewhere.
If we think of the bacterial population as being made up of colonies of bacterial specialists. Some bacteria are efficient at digesting fibre, others sugars or protein. Some of these bacteria are harmful in large numbers but not in small. Simply put, the bacterial population of a healthy rabbit’s digestive system is a balance between good bacteria and bad bacteria. The balance of this bacterial population is influenced by age, diet, season, environment and the use of things like probiotics and antibiotics.
Rabbits are what they eat
In a real sense, the food you feed is the fuel for these bacteria and influences their population numbers. Feed too much of the wrong thing and bad bacteria predominate and cause problems, feed a healthy diet and your rabbits’ digestive system will have large numbers of beneficial bacteria which help your rabbit stay healthy.
Some bacteria produce gasses such as methane during the digestion process. In normal circumstances this is not a problem and is moved out of the body in the normal fashion (keeping in mind that rabbits cannot burp there is only one way out!). Problems with normal digestive function such as blockages, gut stasis, the use of antibiotics or an increase in the population of gas-producing bacteria due to sudden or inappropriate diet changes can lead to bloat. Bloat is a build-up of gas in the stomach, intestines or caecum which can be very painful and can cause breathing difficulties when the gas-filled stomach compresses on the chest and lungs.
You may have heard people who don’t feed a certain vegetable (e.g. cabbage) to their pet rabbits because it causes bloat. The idea that feeding one type of vegetable to all rabbits will make all of those rabbits gassy or bloated is not correct. For reasons that will hopefully seem obvious to you now, the fault lies not solely with the proposed ‘gassy vegetable’ but the body’s (or more specifically the bacterial population’s) reaction to that food, and that reaction will be different from one rabbit to the next to the next. Because each rabbit will have different bacteria in the gut and each bacterial population will have a different level of gas production, there is simply no way to know how your pet will respond to certain foods.
Increased gas production
There are certainly specific foods which can promote gas production, but it is often not the types of things you may think. For example, foods containing high levels of carbohydrates and sugars such as fruits, grains, corn, legumes, starchy foods such as potatoes, or human foods like breads, crackers and cereals promote gas production.
Sweet foods high in sugars and carbohydrates can lead to an increase in bacteria that can be harmful and the glucose which results from the breakdown of these foods can be turned into toxins by certain types of bacteria. These toxins can cause diarrhoea and result in death (this is why your vet tells you to stop feeding these foods to your bunny!). This is particularly surprising when you reflect on many of the treats we see for sale for rabbits. How many of you have seen the corn sticks or seed sticks stuck together with sugary honey? These are not suitable to feed to rabbits.
How do rabbits acquire the healthy bacteria in their gut in the first place?
Baby rabbits get the bacteria from eating both the hard faeces and the caecotrophs their mother produces. Therefore, having mum on the sort of diet that maintains a healthy digestive bacterial population has a direct influence on the health of her offspring.
You may have also heard people say not to feed greens to baby bunnies until they are older as it may cause bloat or diarrhoea. In the wild, baby rabbits would be getting access to small quantities of a large variety of different plants which are usually high in fibre and low in carbohydrate from a few weeks of age.
Pet rabbits unfortunately are often restricted for fear of causing bloat or diarrhoea. So around about the time when our young pet rabbits need to be eating a good selection of foods to encourage a diverse family of bacteria to colonise their gut and an increasingly variable diet as fuel for that bacterial population …. humans come along and say “don’t feed this vegetable, that herb or weed or root etc. as it will cause bloat or diarrhoea” and then give the baby rabbit a lovely big bowl of carbohydrates (muesli mix) instead! This in turn promotes the growth of the types of bacteria we are trying to avoid and in severe cases can result in the death of the baby rabbit.
Will eating a varied diet of greens at a young age cause diarrhoea?
This is very unlikely, but it is dependent on the bacterial population that rabbit has (and probably that of its mother). The key to promoting normal gut bacteria and a healthy digestive system in any rabbit is small amounts of different greens (not a large quantity of any one thing) given gradually. For example, when introducing my hand-reared litter to solid foods, I chose foods which were high in fibre (grass and hay) and fed small quantities of different grasses and hays, then gradually added in two or three types of dark green leafy vegetables and fed that mix daily for 3 – 5 days before adding in the next new item. I also added to the variety by feeding more natural foods such as dried fruit-tree leaves or twigs, weeds, roots and herbs. One of the most wonderful experiences of owning rabbits is to offer different varieties of things and work out what they love! Just be careful not to get stuck feeding the same vegetables over and over again (and let’s be honest we are all guilty of that!) as it is not the best way to maintain a healthy digestive system.
There is a lot of confusion over what things can be safely fed to rabbits so I would encourage you to go to the Rabbit Welfare Association and Fund’s webpage for a list of things that are safe to feed. When thinking about what is likely to be healthy for your rabbit it doesn’t hurt to think about what they would have access to in the wild and try in part to emulate that. The most important thing to stress is that access to large quantities of grass and hay are vital to your rabbit’s health. Fruits should be kept to an absolute minimum and only really given as a treat once a week at most (in very small quantities). Human foods or foods high in sugars and carbohydrates such as corn, legumes and grains should never be fed.
The digestive system plays such a central role in the health of your rabbits in general. The best way to protect your rabbits from many of the major health problems we see such as dental disease, diarrhoea, dirty bottom and flystrike, urine sludge, gut stasis, obesity and from the negative effects of some antibiotics, is to have them on a healthy grass and hay based diet with small quantities of a very large variety of vegetables and other fodder for enrichment.
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Ylvie Combes, Rory Julien Michelland, Valérie Monteils, Laurent Cauquil, Vincent Soulié, Ngoc Uyen Tran, Thierry Gidenne, Laurence Fortun-Lamothe; Postnatal development of the rabbit caecal microbiota composition and activity, FEMS Microbiology Ecology, Volume 77, Issue 3, 1 September 2011, Pages 680–689.
Zhu, Y., Wang, C. & Li, F., 2015. Impact of dietary fiber/ starch ratio in shaping caecal microbiota in rabbits. Canadian Journal of Microbiology, 61(10), pp.771–784.