Chemical Immobilization for Elk
Elk (Cervus elaphus canadensis) are the largest subspecies of red deer (Cervus elaphus), found in North America and in the high mountains of Central Asia. Also called wapiti, elk are members of the deer family, Cervidae (order Artiodactyla). Recent genetic studies suggest that the red deer may actually be three species: the European red deer, the Tibetan–West Chinese red deer, and the elk.1 Exceeded in size only by the moose, large male elk in the northern U.S. and Canada average 380 kg (840 pounds), with some bulls exceeding 500 kg (1,100 pounds) in weight. Bulls in the southwestern U.S. average about 110 kg (240 pounds). Female elk are more similar to bulls in external appearance and body mass than other deer subspecies.
In Europe, “elk” is the common name for the moose. In 16th-century Virginia, the name was adopted by English settlers for the native subspecies of the red deer. The name “wapiti” is actually Shawnee for “white deer” and comes from the light colored coat of the bull elk.2 Today in North America, “elk” is the established proper name for this subspecies.
Elk Biology and Behavior
Elk are essentially red deer in their biology, but they have become adapted to life in open plains, grazing and to long, cold winters. Elk have evolved as fast endurance runners that are very difficult to catch even with horses and motor vehicles, particularly in broken terrain. North American elk are uniform in coat markings and thus cannot be differentiated by these features from some of their Asian counterparts, but they differ from other subspecies of Asian elk, such as the Manchurian red deer (Cervus elaphus xanthopygos) and the Alashan wapiti (C. elaphus alashanicus) of Inner Mongolia. These elk have smaller bodies and antlers, more subdued coat patterns and a deeper voice than North American elk. However, all male elk, American and Asian, have a high-pitched bugling call used during the rut.1
Elk have longer gestation periods than red deer, and bulls retain their antlers longer. In Asia, elk are confined to cold grasslands found on the high plateaus of Outer Mongolia, southern Siberia, and the Altai and Tien Shan mountains. In North America, where there are less competing red deer, elk are found in diverse habitats from the Yukon to northern Mexico and from Vancouver Island to Pennsylvania.2 Elk typically thrive in the coniferous rain forests of the Pacific coast, prairies, aspen parklands, sagebrush flats, eastern deciduous forests, the Rocky Mountains, and the valleys of California. Due to their wide distribution, elk from different regions in North America can differ considerably in size and antler growth.
Elk are believed to be one of the Siberian Ice Age species that crossed the Bering land bridge into Alaska over one million years ago, but were unable to establish themselves in the southern half of the continent due to an overabundance of native large fauna at that time.
Management and Capture Practices
Elk continue to be an important source of food and recreation in and near many of the habitats they occupy, as well as being an important component of rural economies. However, elk populations fluctuate significantly over time, leaving biologists trying to understand the relative contribution of the various causes of population fluctuations for the purpose of increasing elk numbers and improving their management. Settlers hunted once-abundant elk populations nearly to extinction in some areas of North America by the late 1800s, prompting officials to launch efforts to rebuild elk herds.2
Population regulation is a central concept in ecology, and an understanding of how animal populations are regulated is vital to implementing effective management and conservation decisions. Crop depredation by wild elk herds is also a frequent concern for natural resource managers, and mitigation of this issue is an important task for wildlife agencies. This has become an even larger concern as humans have continued to encroach upon wildlife habitats. Finally, investigations into chronic wasting disease (CWD), a fatal, contagious prion disease of free‐ranging cervids has raised some alarm over the implications for elk populations.1,2
These and other management concerns regularly necessitate the examination of individual or groups of elk. Considering the size and aforementioned agility and speed of these animals, chemical immobilization remains the safest and most efficacious method of addressing these aspects of elk management.
Drug Formulations for Elk
Capturing and chemically immobilizing an elk (or any wildlife, for that matter) could be the most traumatic incident of the animal’s life, so it is extremely important to justify all capture and trapping events. Additionally, any person involved in the chemical immobilization or capture of wild animals should be trained accordingly. During chemical immobilization and capture operations, a wildlife veterinarian should be consulted as well as being part of the team. Taking part in captures using chemical immobilization is potentially dangerous, and any individual who takes part in a chemical immobilization assumes a great deal of responsibility. The handling of any captured animal should be performed in as careful and expedient a manner as possible to ensure that no trauma, behavioral distress, or unnecessary discomfort can occur.
Federal regulations dictate that research facilities and entities, animal dealers and exhibitors have an attending veterinarian to consult and provide guidance on capture and chemical immobilization procedures and techniques. In the U.S., the Food and Drug Administration (FDA) determines what drugs can be used on certain species, and requires a registration certificate for those using controlled substances. Field technicians who may be using or administering controlled drugs must be working under the supervision of a certificate holder. In most cases, this will be either the institution conducting the procedure(s) or the attending veterinarian.
Many classes of compounds, including anesthetics, analgesics, sedatives and tranquilizers have been used to immobilize wild animals, including elk. Traditionally, free-ranging elk have been immobilized using potent opioid analgesic compounds. Relatively small doses of opioids can effectively subdue large wildlife species, and can be antagonized for rapid recovery. If handled improperly however, opioids can be hazardous to humans, often limiting their use in the field.
Opioids have three advantages when used to immobilize wildlife:
- They are easy to administer
- They have a high therapeutic index, and
- There are readily available antagonists to reverse their effects.
For the immobilization of elk, Chemical Immobilization of Wild and Exotic Animals. (Nielsen, 1999) recommends etorphine in total dosages of 1-7 mg combined with 15 to 300 mg xylazine. Another regime calls for carfentanil in total dosages of 0.3 – 4.5 mg with or without xylazine.4 Carfentanil is a highly potent synthetic opioid that has been reported to be 50 to 100 times more potent than etorphine.3 These drugs may be reversed with naltrexone (hydrochloride), an opioid receptor antagonist.
The Handbook of Wildlife Chemical Immobilization (Arnemo & Kreeger, 2018) lists the BAM formulation (butorphanol, azaperone and medetomidine) as the most efficacious drug combination for the immobilization of elk. For an adult elk weighing between 230 and 318 kg, the authors recommend butorphanol at 46 mg plus azaperone at 30 mg plus medetomidine at 18 mg. This may be reversed with atipamezole at 25 mg plus tolazoline at 600 mg.5
1Sergeyev M., McMillan B.R., Hersey K.R., Larsen R.T. (2020) The influence of habitat use on harvest vulnerability of cow elk (Cervus canadensis). PLoS ONE 15(11): e0242841.
2nps.gov.
3Johnson, Bruce & Wisdom, Michael & Cook, John. (2004). Issues of Elk Productivity for Research and Management. North American Wildlife and Natural Resources Conference. 69.
4Nielsen L. Chemical immobilization of wild and exotic animals. Iowa: Iowa State University Press, 1999; 227-281.
5Arnemo, J., Kreeger, T. (2018). Handbook of Wildlife Chemical Immobilization 5th Ed.
About NexGen Pharmaceuticals
NexGen Pharmaceuticals is an industry-leading veterinary compounding pharmacy, offering sterile and non-sterile compounding services nationwide. Unlike other veterinary compounding pharmacies, NexGen focuses on drugs that are difficult to find or are no longer available due to manufacturer discontinuance or have yet to be offered commercially for veterinary applications, but which still serve a critical need for our customers. We also specialize in wildlife pharmaceuticals, including sedatives and their antagonists, offering many unique options to serve a wide array of zoo animal and wildlife immobilization and anesthesia requirements.
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