Compared to dogs, cats or humans, rabbits have a much more complicated digestive system, and have to work much harder for their nutrition. The reason for this is simple – diet.
Cats are exclusive carnivores, while dogs and humans are also adapted to obtain the bulk of their nutritional requirements from meat. (Yes, really – the stomach and intestines of a human are virtually identical to that of a wolf, and are fantastically badly evolved for coping with vegetable matter. That’s why we have to pre-process our food, e.g. by cooking, to reduce the amount of work our intestines have to do).
A rabbit, on the other hand, is adapted to eat grass (sorry to shatter an illusion, but carrots and other root vegetables are like junk-food to a rabbit and should be fed only as special treats – grass is much better for them!). However, grass is much less nutritious than meat is, and it takes a lot more work to extract usable material from it.
Roughly 25% of grass is composed of fibre, mainly cellulose and lignin – and no animal on earth can digest these compounds, they just don’t have the cellular machinery to do it. However, many bacteria can, and that’s how a rabbit gets the bulk of their energy. While the stomach and small intestine are basically similar to a dogs, or ours, and excellent at digesting protein and sugar, there’s very little of either in grass. The large intestine of a rabbit, however, is much more complex. The rabbit’s caecum (in dogs a tiny little sac, in humans little more than the attachment for the appendix) is enormous – it’s the largest organ in the abdomen! Inside this fermentation vat, various bacteria live and break down the fibres (that are indigestible to us) into chemicals called “volatile fatty acids”, which can be absorbed into the bloodstream and used for energy, the same way we use sugars.
However, here’s the rub – food can’t stay in the large intestine for long, because it needs to make room for more grass passing down from the head end. As a result, the food in the caecum is only partially digested by the time it’s forced on down the intestinal path, and ultimately excreted.
This is where rabbits get REALLY clever. The colon and rectum (the end of the large intestine) are capable of dividing up the material that they receive, and passing the partially digested bits (that still have lots of goodness in them) as caecotrophs. These “night faeces” are much softer and almost jelly-like, and you’ll never see them lying around in the hutch or bedding of a healthy bunny – because the rabbit eats them directly from his bottom and swallows them.
Now, this may sound utterly gross (and for us it would be – we’re not adapted to do that!), but for a rabbit, it’s essential to their survival. This is because on its first passage through the intestines, the grass only releases 40% of the energy the rabbit needs to survive. The remaining 60+% of the nutrients are locked up in that high protein, high energy caecotroph, which the large intestine cannot digest. BUT… the stomach and small intestine can. So, the bunny gets a second chance at it, releasing the extra protein
and calories the same way a dog, a cat or a human would. It really is a fantastic system! The droppings you see on the floor of the hutch are the true faeces – what’s left when the food has passed through twice, that are filtered out and excreted for good by the large intestine.
As with so much else, it all comes down to diet, and the clever things a rabbit’s large intestine can do!
Rabbits should eat their own body size in good quality hay daily; pellets or other concentrated food should only make up 30g per kg bodyweight per day. Also, don’t feed muesli-style mixes – rabbits tend to pick and mix their favourite bits and often develop dietary imbalances.
If you’re worried about your rabbit’s diet, or any aspect of their health, make an appointment to talk about it with one of our vets!
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