Capture Myopathy in Axis Deer During Capture and Chemical Immobilization

Capture myopathy can occur in both wild and domestic animals. It is a very dangerous condition that involves muscle damage resulting 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 natural causes, such as in prey animals attempting to avoid or struggling with predators.² This condition is of particular concern 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, though it is believed that some species may be more predisposed to it than others due to their temperament and physiological characteristics.³ Capture myopathy has been most widely studied in ungulates and birds, although it can potentially affect any captured wildlife species.² Ungulates in North America that have been reported with capture myopathy have included white-tailed deer, mountain goats, bighorn sheep, pronghorn antelope, bison, moose, and elk.^2,7

Axis Deer: Background and Biology

There are seven species of deer and many sub-species that are native to North America. There are certain species of deer in North America that have been introduced (non-native), and some interbreeding between species occasionally takes place. Deer belong to the order Artiodactyla, and to the family Cervidae. Cervids differ from other ruminants in that males grow antlers that are comprised of bone. These are shed and regrown annually.

The deer family is further divided into two groups—Old World deer (subfamily Cervinae) and New World deer (subfamily Capreolinae). This distinction reflects where these animals evolved, but is not a geographical one. Instead, it references the differing foot structures of the two subfamilies. In Old World deer, the second and fifth hand bones have almost completely disappeared except for proximal, terminal remnants. In New World deer, these remnants are distal.^6,7

The axis deer (Axis axis), also known as the spotted deer or chital deer, is a deer species that is native to the Indian subcontinent. It is a moderately large, spotted deer that was introduced into the southwestern U.S. (Texas) in the early 1900s. Axis deer prefer sparse, secondary forests that supply adequate drinking water and shade, tending to avoid rugged terrain. Their food consists largely of grasses.^4,5

Axis deer are gregarious, and usually are found in herds ranging from a few animals to more than 100. Herd leaders are usually mature, experienced does. Unlike native North American deer, adult male axis deer are normally found living with herds of young and old animals of both sexes. Like elk, rutting male axis deer emit bugle-like bellows, and both sexes can produce alarm calls.⁶

The reproductive pattern in axis deer very similar to that of domestic cattle. In the wild, mature bucks in rutting condition may be found throughout the year, with each buck apparently having an independent reproductive cycle of its own, which may not be synchronized with that of other bucks in the herd.⁴ Females experience estrous cycles throughout the year, with each cycle lasting approximately 3 weeks. While pregnant females may be found year-round, most breeding lasts from mid-May through August. Bucks make no attempt to collect harems of does.

Only one axis deer fawn is produced after a 210 to 240-day gestation period. In Texas, fawns are born in early January to mid-April, although they may arrive in any season. Fawns begin consuming green forage by 5 weeks of age, and are weaned at 4 to 6 months.⁵

Capture Myopathy: Clinical Signs

As indicated earlier, capture myopathy can occur naturally when a deer is attempting to avoid predation. For the purposes of this discussion however, it will be the result of these animals being captured and/or immobilized with or without chemical means being involved. Axis 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 an Axis 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.⁴The 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 Axis Deer

Since there is no treatment for capture myopathy, prevention is 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 (such as large ungulates). An anesthetic protocol consisting of good anesthetic agents can aid significantly in preventing capture myopathy in Axis 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 immobilization event.

The capture team should be aware of the risks for capture myopathy and make every effort to prevent its occurrence. Axis 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 being captured, 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