Unlike dogs and cats, obese rabbits are not prone to the development of diabetes (Harcourt-Brown, 2012) however, obesity can predispose them to many other health issues. The pathogenicity of obesity in rabbits is quite complex with many obese rabbits presenting with a combination of any of the following problems:
The impact each of these conditions has on the rabbit depends on their chronicity and severity and each rabbit on presentation to the clinic will need varying degrees of intervention to correct underlying illness before a weight loss programme can be instituted.
Cessation of caecotrophy — rabbits thrive on high quantities of low nutrient fodder such as grass. The adaptation that allows rabbits to gain sufficient nutrients from such low nutrient material is caecotrophy. This strategy involves the essential but indigestible fibre passing rapidly through the gastrointestinal tract to be excreted as waste in the form of small, dry faecal pellets. The digestible material is passed retrograde into the caecum to undergo bacterial fermentation to extract more nutrients. After undergoing further microbial digestion this ingesta is formed into caecotrophs which are released from the caecum and eaten directly from the rectum. As highlighted by Flecknell and Meredith (2006), caecotrophy provides rabbits with many essential nutrients including:
Obesity can result in the inability to perform caecotrophy. This can result in deficiencies in vitamins B and K and lead to malnutrition. There is also a huge risk of fly strike from the physical presence of caecotrophs accumulating around the perineum.
Diarrhoea — inappropriate diets such as those high in carbohydrates and low in fibre can cause the proliferation of pathogenic bacteria in the gastrointestinal system of the rabbit leading to the development of diarrhoea. High carbohydrate diets such as muesli mixes also predispose to obesity.
Gastrointestinal stasis — gastrointestinal stasis is not uncommon as high carbohydrate and low fibre diets predispose to both ileus and obesity. Ileus develops as a result of high levels of carbohydrates suppressing the release of motilin, a hormone which promotes peristalsis (Flecknell and Meredith, 2006).
Urin scalding and cystitis — urine scalding and cystitis occur more readily in obese rabbits due to accumulation of perineal fat inhibiting urine evacuation, inactivity leading to precipitation of calcium salts in the bladder (sludgy bladder) and difficulty assuming the normal position for micturition (personal experience).
Fly strike — fly strike is seen commonly in obese rabbits as a result of an increased risk of diarrhoea, caecotroph accumulation and urine scalding.
Pododermatitis — pododermatitis is an inflammatory condition usually affecting the hind feet of rabbits. It ranges in severity from mild erythema to severe ulcerations and osteomyelitis. The condition is caused by an avascular necrosis usually as a combination of obesity and incorrect flooring or soiling of the environment.
Arthritis — rabbits have a very light skeleton compared with most species. Their smaller mass facilitates a rapid escape from predators. Obesity expunges millions of years of evolutionary adaptation for flight as a strategy for predator avoidance. Excessive weight on such ‘light scaffolding’ can lead to or exacerbate arthritis and places considerable pressure on joints.
Renal lipomatosis — obesity can cause an accumulation of adipose tissue in the kidneys which may lead to alterations in renal blood flow and lymphatic drainage (Dwyer et al, 1995).
Atherosclerosis — atherosclerosis can occur in obese rabbits that develop higher circulating levels of cholesterol and triglycerides in their blood stream. Plaques containing inflammatory cells, cholesterol, triglycerides and calcium deposits accumulate in the walls of the arteries reducing their distensability and altering blood flow and pressure (Reusch, 2005).
Dental disease — increased risk of dental disease is seen in rabbits eating the high carbohydrate low fibre food which predisposes to obesity. The teeth of rabbits grow continuously as an adaptation to a diet containing abrasive foods such as hay and grass. The walls of such plants contain silica which acts as sand paper for the teeth. The grinding, side to side chewing pattern rabbits adopt when eating grass and hay promotes teeth wear. When a diet high in carbohydrates and low in fibre is fed (e.g. muesli or excessive levels of pellets) rabbits’ teeth are not worn and teeth overgrowth leads to the development of dental disease.
Anaesthetic risk — increased anaesthetic risk is encountered in any obese rabbit presented for even routine surgery. Spey operations in particular become more difficult as much of the intra-abdominal fat is stored in the broad ligament of the uterus. This makes the uterine vessels difficult to visualise.
Hepatic lipidosis — hepatic lipidosis can result when obese rabbits have a sudden reduction in calories either through food restriction or anorexia from ill health.
Pregnancy toxaemia — pregnancy toxaemia is seen in obese pregnant rabbits who suddenly become anorexic or where food intake is restricted. Does in a negative energy balance rely on fat stores for energy which results in hepatic lipidosis as the liver is unable to process the large volumes of fat. The production of ketones through fat metabolism leads to a metabolic crisis. It is a life threatening condition to the doe and her young (Flecknell and Meredith, 2006).
Hyperthermia — hyperthermia is more common in obese rabbits exposed to high temperatures. Rabbits do not tolerate temperatures in excess of 20°C (68°F) well.
Causes of obesity
The most common factors leading to obesity in rabbits are reduced activity level (often due to restricted access to space) and feeding of a highly calorific diet such as muesli, excessive pellets and low levels of grass and hay (Figure 1).
Lack of exercise
One of the major welfare concerns of rabbits is the lack of space many rabbits have access to as highlighted by The Rabbit Welfare Association's A Hutch is Not Enough campaign (Rabbit Welfare Association http://www.rabbitwelfare.co.uk/ahutchisnotenough.htm). A study by Dixon et al (2010) showed that the larger the space a rabbit is placed in the more it moves around and interacts with that environment. Rabbits in smaller spaces were observed to be much less active. Current recommendations from the Rabbit Welfare Association are a hutch of minimum 6 foot long, 2 foot wide and 2 foot high. This should be attached to an 8 foot long, 4 foot wide and 4 foot high run.
Sourcing appropriate sized hutches and runs can be difficult with many of those available on the market not meeting the minimum size recommended. There are however, many retailers signing up to the Rabbit Welfare Association's charter pledging to make appropriate sized enclosures (http://www.rabbitwelfare.co.uk). Additional space for rabbits can be achieved with one of the innovative, predator proof modular set ups available on the market (http://www.runaround.co.uk). Sadly, many rabbits are not given access to enough space and have no opportunity to exercise. This not only predisposes to obesity, it also impacts negatively on their mental health.
Diet
When discussing the issue of diet with clients it is important to make the distinction between what is being offered to the rabbit and what is being eaten by the rabbit. Rabbits are notorious selective feeders. When given the opportunity to pick out the sweet, high calorific, low fibre and high carbohydrate components of a varied diet they will do so readily (Prebble and Meredith, 2014). Rabbit obesity usually occurs as a result of one of the following:
Obesity is never as a result of a rabbit that has managed to gorge itself on hay or grass!
The ideal diet
Endeavour to keep things simple when making recommendations to clients. The author prefers to talk in measurable, easily quantifiable amounts rather than percentages of total diets.
The eventual goal for a healthy, adult 2 kg rabbit is:
Extrapolations can be made from this for smaller and larger rabbits but recommendations should be based on the individual animal's body condition score and weight and activity levels.
Identifying obesity
The first step in combating the problem of obesity in rabbits is recognising it. There are several methods for assessing bodyweight that are currently applied in general practice including weight charts and body condition scoring. Bodyweight charts with listed weights of certain breeds of rabbit are not particularly useful. There is too much variability within breeds and many of the rabbits presented are crossbreds.
Body condition scoring (BCS) the subjective assessment of adipose tissue coverage in localised regions through palpation and visual criteria is a commonly used system in dogs and cats (German et al, 2006) and has been described in rabbits (Reusch, 2010). There are several different scales in common use including the Pet Food Manufacturers’ Association rabbit size–o-meter (http://www.pfma.org.uk/rabbit-size-o-meter/) which uses a scale of one (emaciated) to five (overweight) (Figure 2).
A zoometric index theorised by Sweet et al (2013) using the ratio of bodyweight to distal forelimb length was found to be accurate for rabbits of medium size. The measurements are taken with a standard set of scales and a tape measure. Forelimb is measured from the lateral surface of the olecranon to the dorsal surface of the nail bed of digit two. A ratio of the distal forelimb length and bodyweight in kg is then assessed using a chart which correlates the ratio with body condition scores.
Both the zoometric ratios and body condition scores are useful but have in common the fact that they are prone to error in inexperienced hands. To avoid problems it is important that rabbits are assessed by someone familiar with these techniques. The development of a specialised clinic for the evaluation and treatment of obesity in rabbits is recommended by the author.
How to achieve weight loss
A gradual weight loss of 0.5–1.5% of bodyweight per week is advised (Reusch, 2010). Sudden dietary changes are not recommended as they may lead to inappetance and digestive upsets. Rabbits eating muesli mixes should be gradually transitioned onto a high fibre pelleted ration.
The Rabbit Welfare Association and Fund has a list of safe plants and vegetables to feed (http://www.rabbitwelfare.co.uk/resources/content/info-sheets/safefoods.htm) which would be helpful to provide to clients to ensure low nutrient vegetables are offered in favour of fruits or root vegetables high in carbohydrates. During the weight loss programme fruit should be avoided. In rabbits of ideal weight, fruit should only be fed once or twice weekly; the author recommends three 1 cm x 1 cm cubed portions of a fruit at each offering.
Depending on the particular case the first step in achieving weight loss may just be cutting out all the inappropriate human food, fruit and treats the rabbit is fed. The author advises completely avoiding commercial rabbit treats as many of them contain high carbohydrate foods stuck together with sugar. Instead, offer small bunches of fresh herbs or a variety of dried forage available from places such as Galen's Garden (http://www.galensgarden.co.uk). Recheck the rabbit every 2 weeks initially and monitor weight loss.
During the second phase, gradually reduce the amount of commercial rations over a 2 to 4 week period. During this time a food diary and careful weight monitoring are essential. Some rabbits may completely refuse to eat hay and owners need a lot of support to persist. Many owners struggle to encourage hay eating from their pets as they perceive hay to be a very boring food source.
For reluctant hay eaters, provided it has been established there is no underlying health reason for hay refusal (e.g. dental disease) the following should be considered:
Try presenting hay in different ways using hanging baskets and hay racks, or twisting fresh herbs into the hay or hide herbs in the middle of a hay ball. Disperse the day's ration of pellets and vegetables amongst the hay if necessary.
Weight loss clinics
Owners should be given appropriate advice and the weight loss of their pet monitored carefully to avoid rapid weight loss and development of problems such as hepatic lipidosis. Evaluation of body condition scores and zoometric weight ranges should be undertaken by those familiar with the techniques. Weight loss clinics are essential to achieve safe, successful weight loss.
Once the rabbit has reached its desired weight, teach the owner how to body condition score and encourage them to regularly weigh their pets. Health checks including weight assessments should be encouraged several times a year.
Conclusion
Obesity in any animal is deplorable but particularly so in a species whose survival mechanism depends on them being lithe. Owners are usually responsible through a combination of ignorance and a desire to spoil their pet — with the best of intentions. Establishing a dedicated weight loss clinic where it is possible to provide simple, practical advice and channel the owner's need to care for their pet by encouraging environmental enrichment and improved husbandry will make for much healthier, happier rabbits.