Capture Myopathy in Deer During Capture and Chemical Immobilization

Capture myopathy is a dangerous condition that can occur in wild and domestic animals. It is described as muscle damage resulting from extreme exertion, struggle, or stress. This condition 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 Capture myopathy 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.^2,5

Deer Background and Biology

Deer belong to the order Artiodactyla, hoofed mammals with an even number of toes on each foot. They are also commonly referenced as cervids. Deer are herbivores who browse for roots, twigs, bark, grass, leaves, and other vegetation. They have a four-chambered stomach, one of which (the rumen) stores undigested food that is later passed back into the mouth, where it is chewed and swallowed a second time. This gives ruminants like deer the ability to take in a large quantity of food and retire to a safe place to chew it thoroughly.³

Cervids differ from other ruminants in that males grow antlers that are comprised of bone. These are shed and regrown annually, and increase each year in size and intricacy. Except in the case of caribou, female deer do not grow antlers. While the antlers grow, they are covered by a thin layer of downy skin known as velvet. When the antlers are fully grown, the velvet dries and is typically rubbed off by the animal.³ Antlers serve as ornamentation for breeding purposes, as well as weapons during the mating season.

Seven species of deer are native to North America, with many existing sub-species. There are certain species of deer in North America that are not native, and some interbreeding between species occasionally takes place.⁴ Deer have a range that blankets the North American continent, making them popular among big game hunters and, more recently, deer farmers. Currently, there is an estimated 36 million deer in the United States. In some states, deer are so plentiful that regular hunting is needed to preserve the ecosystem.

The Whitetail Deer (Odocoileus virginianus) is the most widely distributed deer in North America, with a range that extends east from the Rocky Mountains into Mexico.⁴ These animals can reach a length of approximately six feet and a height of approximately three feet at the shoulder. Adult males (bucks) can weigh up to 180 pounds, while females (does) average between 80–120 pounds.

Other deer that are widely distributed in North America are the Mule deer (Odocoileus memionus), Caribou (Rangifer tarandus), Moose (Alces alces), Elk (Cerbus canadensis) and the Brocket deer (Mazama gouazoubira).

Clinical Signs of Capture Myopathy

Capture myopathy can occur naturally when a deer is 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. Deer 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 can result.²

Clinical signs of capture myopathy in a deer 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 capture myopathy. 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 capture myopathy. The increase in body temperature can be above 42°C.⁴ Muscle spasms, stiffness and lameness are also clear signs of capture myopathy. 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. Upon necropsy, light-colored skeletal and cardiac muscle is indicative of capture myopathy being the cause of death.

Preventing Capture Myopathy in Deer

There is no treatment for capture myopathy. Thus, 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 deer. In the case of wild deer (as opposed to a zoo or farm), the remote delivery of anesthetic agents is considered a superior methodology to trapping 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. Deer 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 protocols for chemical immobilization may vary depending on the deer species, 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 not a guarantee of avoiding capture myopathy in any deer.³