Let us start by looking at the rabbit, guinea pig or chinchilla as a machine, so we understand the mechanics of it. Food goes in one end and droppings come out the other. That much is obvious. This is a guide to the mechanics of what goes on in-between and helps explain why those who know about these animals place such emphasis on feeding ad lib quality hay.
The wild rabbit, guinea pig or chinchilla is designed to eat large amounts of high fibre food, mainly grass, wild plants, bark and buds.
Stage 1. Cutting and grinding.
The mouth – Food is cut by the front incisor teeth. This is an up and down movement of the jaw. Then the cut pieces are moved onto the back teeth and ground down. This is a side to side movement. Particles of chewed hay and grass are normally around 5mm long, the ideal size for stage 2.
Stage 2. Disinfection and pre-digestion.
The stomach – Food particles form a loose ball in the stomach. The rabbit, for example, only has a small stomach which simply empties into the small intestine when there is enough bulk to force it there. The loose texture of this ball allows the gastric juices to permeate it easily. These juices are acidic, pH 1-2, and this acidity helps kill any bad bacteria that might be lurking on the food. The long fibre also helps speed the passage of food through the rabbit’s digestive system.
Stage 3. Separating the digestible and indigestible elements.
The Rabbit’s GI Tract – Speeding through the small intestine, the ball arrives at the caecum and proximal colon. The wall of the caecum is designed to pick up the digestible nutrients in small pockets and to concentrate the indigestible fibre into the centre through muscular contraction. Indigestible particles are sent down to be processed into hard waste droppings and the digestible ingredients fermented by the good bacteria in the caecum into amino acids (protein), fatty acids (energy) and B vitamins. Some of these are absorbed directly into the blood stream but most are converted into the soft caecotrophs that the rabbit eats direct from the anus as they are produced.
Little and often
The way a wild rabbit eats is to nibble on grass or similar food for a couple of hours twice a day. This food is essentially 10 or so small meals in the sense that the rabbit’s small stomach may fill and empty 10 times, but it is essentially one big morning and evening banquet! For the first four hours after each banquet the rabbit will produce regular waste droppings. Then for the next four hours it will produce and reingest the soft pellets produced in the caecum.
The mucus covering on these soft droppings protects the good bacteria from the acid environment of the stomach for about 6 hours. This second, recycled feast, is more easily broken down into the amino acids for body building, fatty acids for energy and essential B complex vitamins. This can be done in the safety of the burrow, away from predators.
If a rabbit is on a high fibre diet or lacking in energy for some reason it will eat all the caecotrophes it produces. On he other hand if it is on a diet rich in protein or energy it will leave some.
The digestive process
From the workings of this machine it is easy to understand the Food In – Droppings Out process in action. Now we need to look at it in smaller detail.
The rabbit takes in Food which is combined with Fluid (stomach acid and water) and broken down by Flora (the good bacteria in the caecum) and then separated into Fuel and Fibre.
Things which can go wrong within this process
- Not enough rough food to keep the teeth in trim. Rabbits teeth grow continuously and if they are not used on a regular basis for intensive periods of cutting and chewing then spurs can grow on the molars leading to painful soft tissue in the mouth and root overgrowth, sometimes even penetrating the jaw. Elongated incisor roots can impinge on the tear duct, leading to weepy eyes and infection. When combined with selective breeding that can lead to congenital deformity of the jaw and calcium deficiency which can cause degeneration of the jaw bone supporting the tooth in its socket, it is easier to see why these conditions are so common.
- Not enough long fibre to create an open ball of food in the stomach. Although particles of chewed grass or hay are 5mm long, the fibre in pellets is cut much smaller and there is little fibre in grains and biscuits. These produce denser balls which makes it harder for the stomach acid to penetrate and kill any bad bacteria. In addition, the shorter the fibre, the slower the process through the gut. Instead of taking 4 hours as in the case of grass or hay, fibres 3mm or less can take over 14 hours to pass through the rabbit. The time taken for food to be processed is known as ‘transit time’.
- Long transit time leads to dehydration of the food ball. All food balls contain hair from normal grooming which is simply passed in the faeces. When the food ball dehydrates however it can lead to the formation of fur balls. Fur balls are even more likely if the rabbit is obese, inactive and doesn’t drink enough water. The average rabbit takes in 10% of its bodyweight in water every day. Easy to see how the lifestyle of the average rabbit could contribute to this health problem.
- Slow transit time through the caecum and high levels of starch and sugars alter the pH of the gut in favour of disease causing bacteria. Although bacterial infection of the gut is unusual in adult rabbits because of the natural acidity in the gut, in young rabbits not only is the pH of the gut almost neutral pre-weaning but it is also lacking in natural gut bacteria until they are 4-6 weeks of age. In newly weaned rabbits, 4-8 weeks old, this combination can expose them to the risk of the most severe form or enteritis.
- Low fibre, protein-rich diets also create more caecotrophes than the rabbit will eat. If the rabbit is also obese it will find it harder not only to ingest essential caecotrophes but also fail to remove them leading to mucky bottom and the risk of fly strike in the warmer months.
It’s an all too familiar story. “My bunny stopped eating, and then she just died.” When we ask for details, we often learn that not only did the bunny stop eating, but she had been producing extremely small or even no fecal droppings, or showed symptoms of “runny stool.” Gastrointestinal Stasis,the Silent Killer by Dana M Krempels PhD, University of Miami
The mystery of rabbit poop Another articles by Dana M Krempels PhD,University of Miami in which she describes the two different types of droppings rabbits produce and what can go wrong in the digestive process. How these dietary issues manifest and how bacterial and other infections affect the rabbit’s droppings.
Rowett Institute’s Rumen-Up Project – May be of interest to researchers