LINKS BETWEEN DIET AND DISEASE.

Low fibre and high carbohydrate diets are linked to dental disease, gastrointestinal disease, obesity and behavioural problems. Excess calcium in the diet can be linked to urolithiasis (bladder stones).

1. Dental disease Rabbit teeth grow constantly throughout life. The rate of growth should balance the amount of wear produced by grinding fibrous foods, so that tooth length stays constant. Incisor wear, growth and eruption are balanced in a normal rabbit at a rate of about 3mm per week. Food is ground by the cheek teeth. A natural diet of grass and plants is highly abrasive to the cheek teeth, so there is rapid wear of the teeth, around 3mm per month, with equally rapid tooth growth. Upper teeth grow faster than lower teeth, which is why problems are generally seen first on the upper jaw.

Rabbits on a high carbohydrate and low fibre diet have reduced tooth wear and therefore elongation of the tooth both above and below the gum. This results in irregular wear, distortion and the formation of sharp painful spikes. Severe elongation of the cheek teeth can prevent the mouth from closing fully, which ultimately prevents the incisors meeting properly, causing them to also overgrow. Overgrown distorted teeth are predisposed to infection and the development of facial abscesses.

High carbohydrate diets and reduced wear also predispose to caries (cavities).

Opinions vary on the significance of dietary calcium levels on dental disease. Many rabbits are selective eaters of coarse mix, favouring items low in calcium and fibre. This can make them prone to osteoporosis, poor tooth and bone quality, and dental disease. Bone growth, development and maintenance is also dependent on the mechanical stresses to which it is subjected and rabbits which do not spend prolonged periods grinding fibrous food can also show poor jaw bone quality. Low vitamin D levels are common in rabbits that have no access to sunlight, and this may also be associated with poor tooth and bone quality. Although rabbits do not need vitamin D in order to absorb calcium, low levels of both calcium and vitamin D are likely to be a significant factor in the progression of dental disease.

Not all dental disease is due to diet, and genetic factors are also important. A congenital malalignment of the teeth, particularly in extreme dwarf and lop breeds, can also be a significant factor.

2. Gastrointestinal disease Fibre is critical to the rabbit for gastrointestinal health because it stimulates and maintains normal motility of the gut. Low fibre diets predispose to gut stasis and the formation of hairballs. Carbohydrates (simple sugars and starches) are an important energy source and are digested and absorbed in the stomach and small intestine. However, any residual starch that is not digested and absorbed in the small intestine passes into the caecum as a substrate for bacterial fermentation. High starch diets can be incompletely digested due to the rapid gut transit times, and cause a rapid overgrowth in caecal bacteria. This can lead to enterotoxaemia and a fatal diarrhoea. This is seen mainly in young, recently weaned rabbits when also fed minimal hay, and combined with the stress of a change of diet and a recent move, for example from a breeder to a pet-shop.

3. Behavioural problems Rabbits in the wild spend many hours a day eating. Low fibre concentrate diets are rapidly eaten and rabbits can develop vices related to boredom, such as increased aggression or repetitive bar biting. Lack of fibre can also lead to fur chewing and barbering.

4. Obesity Fats are used in commercial rabbit diets to improve palatability and provide a non-carbohydrate energy source. Fat also stimulates gastrointestinal motility, but reduces intestinal absorption of calcium. Many treat foods contain high levels of fat, (e.g. chocolate drops) and should not be fed. High fat levels also increase the risk of hepatic lipidosis developing during periods of starvation. Pet rabbits are prone to obesity so high fat diets and ad lib feeding of concentrates should be avoided.

5. Urolithiasis Excess calcium in the diet can contribute to sludgy urine or even urolithiasis (bladder stones), which often require surgical treatment. Rabbits have a unique calcium metabolism in that they do not control uptake of calcium from the gut. Instead, they absorb most of what is eaten and excrete the excess in the form of calcium carbonate, in the urine. Although it is normal for rabbits to have calcium crystals in the urine, overweight inactive animals, those with neurological or other problems affecting normal bladder function and emptying, or those with urinary tract infections seem predisposed to developing problems associated with this.

Substances in foods called phytates, oxalates and acetates form complexes with calcium and other minerals and this can hinder their absorption. Phytic acid is present in high quantities on grains and beans. Oxalates are present in many plants including swede, spinach and alfalfa, in which 20-30% of the calcium is in the form of calcium oxalate which reduces its availability. Feeds high in calcium and low in oxalate include kale, broccoli, turnip, collard and mustard greens.

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