Capture Myopathy in Antelope

Capture myopathy (CM) is a serious condition that can occur in wild and domestic animals wherein muscle damage results from extreme exertion, struggle, or stress. It is also known as exertional myopathy, overstraining disease and exertional rhabdomyolysis.1 Capture myopathy most often occurs as a result of capture, transport or chemical immobilization, but it can also be the result of other natural causes of stress, such as in prey animals attempting to avoid or struggling with predator animals.2 It is of particular concern in cases when it is a cause of death in wild animals that are handled by humans.

Capture myopathy can occur in any animal under extreme stress, although it is thought that some species may be more predisposed to it than others due to their natural temperament and physiological characteristics.³ Capture myopathy has been most widely studied in ungulates and birds, although it is believed to potentially affect any captured wildlife species. It has also been observed in coyotes, badgers, primates, and many other species.² Ungulates in North America that have been reported with this condition have included white-tailed deer, mountain goats, bighorn sheep, pronghorn antelope, bison, moose, and elk.^2,3 It is believed that capture myopathy can even occur in fish and amphibians.¹

Causes and Clinical Signs of Capture Myopathy

Capture myopathy can occur naturally when antelope are attempting to avoid predation, but for the purposes of this discussion, capture myopathy will be the result of these animals being captured and/or immobilized with or without chemical means being involved. Antelope, like other animals, are adapted to escape from predators, but they are not adapted to struggle for long periods of time in human-constructed restraints.³ When animals overexert themselves (e.g., struggling in a trap) to the extent that physiological imbalances develop and result in severe muscle damage, capture myopathy results.² Increased ambient temperatures and repeated chemical immobilization can increase the risk of animals suffering from capture myopathy.⁴

Clinical signs of capture myopathy in the antelope can vary depending on the species and the cause of exertion.² The method of capture and restraint is also a determinant in occurrences of CM. The available literature states that capture myopathy may result in sudden death, or that clinical signs may develop hours, days, or up to two months following capture.⁴ The clinical signs during early onset include elevated respiratory rate, heart rate, and body temperature.^1,3 Body temperature increases during exertion, with higher temperatures being associated with death due to CM. The increase in body temperature can be above 42°C.⁴ Muscle spasms, stiffness and lameness are also clear signs of CM. Animals often become recumbent and may stumble. If dark red-colored urine is noted, this is an indication that the animal's muscles are breaking down and that its kidneys have been severely affected.^2-4 Death of the animal usually follows. If the animal survives the acute stage of the condition, scarring of heart and skeletal muscle tissue may permanently debilitate the animal.⁴ Upon necropsy, light-colored skeletal and cardiac muscle is indicative of capture myopathy being the cause of death.

Preventing Capture Myopathy in Antelope

There is no treatment for capture myopathy, prevention being the best method of avoiding this condition. Care should be taken in case of handling of animals that tend to be more susceptible to capture myopathy. An anesthetic protocol consisting of good anesthetic agents can aid significantly in preventing capture myopathy in antelope. In such cases, the remote delivery of anesthetic agents would be a superior methodology to trapping the antelope prior to the anesthetic event.

The team in the field should be thoroughly aware of the risks of capture myopathy and make every effort to prevent its occurrence. Antelope (and indeed, any wild species) should only be captured when necessary, and the negative effects that capture may have on an animal's health should always be considered before beginning a capture or initiating an anesthetic event.⁵ Capture methods that minimize animal stress, struggling and handling time should be utilized. Appropriate methods may vary depending on the subspecies, so research can be helpful in identifying the ideal capture method. It has been reported that using a combination of Xylazine HCL and Ketamine HCL can decrease the chance of capture myopathy, but this is by no means a guarantee of avoiding capture myopathy in any antelope.³