Muscular and skeletal degeneration in rabbits
that lack exercise
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Wild rabbits are very athletic animals that are built to move rapidly in order to find food, water, find or fight mates, or flee predators over greater distances to find a hiding place. This daily exercise strengthens the locomotive muscles, fortifies their heart and lungs and increases their resistance against stress. Regular movement will fortify muscle and bones, will stimulate the blood circulation, and the activity and functioning of organs including the digestive system.
House rabbits often do not have the possibility to develop as their wild brothers and sisters, as they are often confined in small hutches or cages with poor possibilities to exercise their muscles and develop strength. This will inevitably lead to systemic hypoplasia underdevelopment of tissues or organs) and the development of physiological, physical and/or behavioral disorders.
Physical disorders include:
· Overweight. The lack of exercise needed to burn calories and a rich diet will undoubtedly lead to overweight and accumulation of fat in female and male rabbits. This can lead to the development of (ulcerative) pododermatitis, cardiovascular problems, and skin problems, due to the inability to groom properly.
Physiological disorders include:
· Gastro-intestinal disorders, e.g. decreased intestine motility,
· Cardiovascular disorders, e.g. weak heart muscle,
· Urinary disorders, e.g. soiling of the perianal region, paste-like consistence of urine (sludge) or formation of kidney or bladder stones,
· Pulmonary disorders, due to cardiovascular problems.
Muscular and skeletal problems
When a rabbit is not given opportunities to exercise, the muscle mass will not develop and remain weak. In terrible cases, a rabbit has been found unable to develop a proper motor coordination and normal ambulation.
The heart is also affected and will remain weak. Aside problems of proper blood circulation and blood pressure, a weak heart will lead to problems when a rabbit will face a stressful situation. While a well-trained wild rabbit can cope with the stressful event, like being chased or hunted and will flee over a greater distance to find a shelter, the poorly exercised rabbit, that is confined in a cage, may not be able to cope with the situation and may faint or die from a cardiac arrest.
Lack of exercise furthermore influences the vertebral column. The spine possesses 3 types of muscles connecting the transverse and spinous processes of each vertebra: the transversospinalis muscles. The function of these muscles is not well understood, but is believed to be involved in local rotations of the vertebral column or initiate bending. The fact that some transversospinalis muscles cross a few intervetebral joints suggests a role in the control of the vertebral position and the stability of the spine, fore- and hind- limbs.
The spine is furthermore connected to an intricate system of trunk muscles:
· extensors, which include the back and gluteal muscles (muscles that form the buttocks.), allowing for instance hip movement,
· flexors, which allow the spine to bend, to control the arch of the lumbar spine, or hip movement,
· obliques, that stabilize the spine.
The bone structure and density is often affected in rabbits with lack of exercise and/or a diet deficient in calcium, mineralization of bones is poor. Weakened bones and bones affected by osteoporosis are easily injured or broken. The vertebras of the spine provide support for the back. If this is accompanied by poorly developed transversospinalis spine muscles and trunk muscles, the normal balance of the spinal structure and the biomechanics can be altered, which can leads increasingly to degenerative processes. Deformations appear that will prevent the development of a good locomotric activity. Intrinsic muscle disbalance furthermore leads to degenerative changes of the lumbar vertebrae and of the femoral head have been observed in rabbits that lack exercise. They include:
· hemivertebrae (abnormal birth defect in which the vertebra fails to develop completely. As a result of the growth defect of the spine, a wedge-shaped vertebra develops, and neighboring vertebrae expand or tilt to fit the deformity)
· spondylosis (a condition of the spine marked by stiffness of a vertebral joint)
· kyphosis (humplike curvature of the spine)
· lordosis (abnormal, increased degree of forward curvature of any part of the spine).
The severity of the deformations is shown to depend on the cage size.
Rabbits suffering from weak muscles and poorly mineralized bones and/or bone degeneration are at increased risk of spine fracture when there is an inadequate support of the heavily muscled hindquarters, walking on a slippery floor, or twisting of the lumbosacral junction when frightened or restrained. Fracture is commonly observed at the level of the 7th (L7) lumbar vertebra.
A radiography will confirm the injury or fracture the degree of severity of the problem can be assessed. Each case needs to be evaluated on an individual basis.
Thanks are due to Dr B. Langhofer (The Scottsdale Veterinary Clinic Scottsdale, AZ, USA), and to A. Carpenter for sharing their pictures.
1. Katherine E. Quesenberry, James W. Carpenter, Peter Quesenberry Ferrets, Rabbits and Rodents: Clinical Medicine and Surgery Includes Sugar Gliders and Hedgehogs, Elsevier Health, 2004.
2. Frances Harcourt-Brown Textbook of Rabbit Medicine, Oxford UK: Butterworth-Heinemann, 2001.
3. Paul Flecknell, editor, BSAVA Manual of Rabbit Medicine and Surgery Gloucester, UK: British Small Animal Veterinary Association, 2000. and references therein.