Capture Myopathy

Capture myopathy is muscle damage caused by extreme stress and exertion, usually after an animal has been chased, netted, held, immobilised or transported. You may also see it called exertional myopathy or exertional rhabdomyolysis, which simply means muscle breaking down after overwork. In a panicking animal the muscles work far beyond what their oxygen supply allows, the blood turns acidic, body temperature climbs, and muscle fibres begin to die. The contents of those damaged fibres, including the muscle pigment myoglobin, potassium and muscle enzymes, spill into the bloodstream. The kidneys can be overwhelmed trying to filter them out, and kidney or multi-organ failure is the usual cause of death.

It was first recognised in an antelope in Kenya in 1964 and has since been described in mammals, birds, reptiles and marine mammals, with hoofed animals such as deer and antelope, and long-legged wading birds, appearing most often in the literature. Any animal under severe stress can be affected, and some species are more prone than others because of temperament and muscle physiology. That is why it matters outside conservation work too: rabbits, guinea pigs, birds and reptiles kept as pets retain the same flight response as their wild relatives, and horses suffer a closely related form of exertional rhabdomyolysis. A long chase around the garden, a rough struggle during restraint, or a hot, cramped journey can be enough to tip a frightened animal over the edge.

Signs that warrant an urgent call to a vet after a stressful chase, capture or transport include:

• Trembling, stiffness, weakness or muscles that feel hard and painful
• Difficulty standing or walking, wobbliness, or an animal that sits or lies and will not get up
• Fast breathing, a racing heart or a body that feels unusually hot
• Dark brown or red-tinged urine
• Collapse or sudden death

Timing is unpredictable. An animal may die within minutes, or look reasonably normal and then deteriorate hours, days or even a few weeks later, so a stressful capture is worth mentioning to your vet even if your pet seems fine afterwards.

There is no specific cure. Treatment is supportive and often intensive: intravenous fluids to protect the kidneys and flush out muscle breakdown products, cooling, pain relief, quiet rest and later physiotherapy to help an animal regain its footing. The outlook is guarded at best, which is why prevention carries most of the weight. Keep handling short and calm, avoid prolonged chasing, avoid catching or transporting animals in the heat of the day, use a dark, well ventilated carrier, and ask your vet about sedation for animals that panic badly during examinations. If you find injured wildlife, do not pursue it yourself; contact a vet or a licensed wildlife rehabilitator, who can plan a capture that minimises the struggle.

This is general information rather than advice for a specific animal. If you are worried your pet has been through a frightening capture or transport and is not moving normally afterwards, have a vet assess it the same day.