Chemical Immobilization of Wild Animals—Dosages

One of the most challenging aspects of wildlife veterinary medicine is the process of determining the correct dosages for wildlife species when providing chemical immobilization. Chemical immobilization is a form of animal restraint in which medications are used to restrict the movement and/or response of an animal during procedures.1 When applied correctly and with due precaution, this is a safe and effective capture method. Chemical restraint is often advantageous over physical capture, since it allows for the examination and treatment of sick, injured or study animals. Chemical restraint allows for the restraint of aggressive animals or selected animals within a group.2 Further, the equipment required for chemical restraint is generally far easier to transport in the field that equipment for physical restraint (although both can be necessary in some instances).

While not all wildlife species are commonly studied or treated by veterinarians, those that do find their way into research studies, management programs or in veterinary clinics (due to injury in urbanized areas, for example) are too numerous to mention.

As chemical immobilization protocols have become more refined and drug formulations for chemical immobilization have become more in number, these challenges have only increased.

Wildlife Management

Many, if not most of the chemical immobilization procedures and protocols in use today are concerned with wildlife management and research studies. In short, wildlife management is the science of establishing parameters and attaining various goals by influencing and/or maintaining wildlife habitats and populations.¹ This process involves numerous components, including the following: 

• The current knowledge and understanding of wildlife populations and trends
• Factors that influence wildlife populations
• The interaction of wildlife species
• The impact of humans on wildlife populations
• How surrounding and/or changing landscapes affect wildlife populations²

Wildlife managers are called upon to have a wide range of knowledge about not only the wildlife species within the ranges or areas for which they are responsible, but the characteristics of these ranges and areas themselves. This includes such aspects as carrying capacity (of areas, ranges and regions), ecosystems, habitats and seasonal changes, among many others.¹

Human habitation is also responsible for bringing about changes that impact wildlife species. Because human populations are growing so rapidly, there are increasing incidences of conflict between humans and wildlife species, which of course has a direct impact on wildlife management objectives and goals. These objectives and goals vary from region to region, from species to species, and depend upon the circumstances that arise due to the interplay between human and wildlife populations.

Quite often, the goals of wildlife managers are focused on the preservation of wildlife species within a region. In other circumstances, keeping populations within certain bounds are a key motivator. In still others, preventing conflict between human and animal populations is a concern. In all of these cases, chemical immobilization procedures often come into play for the purposes of health monitoring, relocation and a host of other purposes.³

Research & Exotic Species

Wildlife research is typically concerned with scientific field studies conducted on wildlife species. The objectives and goals of such studies depend entirely upon the researcher or research body involved; these may be private institutions, universities, management bureaus or universities. As such, they involve methods of animal capture, principles and methods of restraint, animal marking, animal transportation and housing, maintenance of wildlife in captivity, translocation and release, animal surgery, blood sample collection, recognition and management of pain and euthanasia.

Wildlife studies vary in their invasiveness and impact on the animals being studied. In all circumstances, researchers seek to minimize any negative impact on the welfare of the animals involved.² Good animal welfare practices for wildlife research is characterized by the same features as laboratory-based research, however different approaches and procedures are needed for wild animals as compared to laboratory-bred animals. Wildlife research is usually conducted with free-ranging animals in their natural habitat or with wild-caught animals in various captive settings.¹

Thus, chemical immobilization and the same dosing concerns which face wildlife managers also apply to those conducting research involving wildlife species.

Traditional Veterinarians and Wildlife

Wildlife veterinarians are licensed animal health professionals who specialize in treating many different types of wildlife. Wildlife veterinarians most often work for federal, state, or tribal fish and wildlife agencies or non-government organizations.² Working closely with wildlife managers and biologists, the job of a wildlife veterinarian is to provide technical expertise to the agency, to conserve and manage fish and wildlife populations, and help to manage endangered species.

Occasionally however, veterinarians in traditional practices (small and large animal) are called upon to treat wildlife species. This often comes about as a result of animals that are injured as a result of their proximity to human habitats, or where the overlap of human habitats requires the temporary intervention of a veterinarian during the course of treatment prior to wildlife managers becoming involved.

Chemical Immobilization and Dosing

Chemical capture can present disadvantages, such as the occasional failure of equipment, undesirable drug side effects or the improper darting of an animal. Nevertheless, chemical restraint has become a valuable tool in wildlife health, research and management, as it facilitates the handling of animals when required for experimentation or medical procedures.⁴

Modern capture methods require a high degree of expertise and experience, as well as knowledge of physiology and behavior of an animal to be captured. One of the key challenges facing wildlife veterinarians is high degree of knowledge needed to address the vast number of variables in treating the relative number of species in the wild.¹ Wildlife veterinarians must be familiar with a wide array of environmental and biological variables while using chemical restraint on wild animals. In order to minimize risks of anesthesia to subject animals, veterinarians also need to be able to react appropriately using the correct equipment with sufficient skill to deal with anything that may go wrong during the capture.¹ Obviously, these variables significantly impact protocols used for dosing wildlife.

There are numerous references in the available literature (scientific studies, etc.) that contain dosing recommendations for various wildlife species. Given the sheer number of species that the wildlife or research veterinarian may encounter combined with the drug formulations now available for chemical immobilization however, determining the right drug at the right dose for a species can present significant challenges.

Fortunately, there are two books that have become the “go-to” references for wildlife managers and wildlife managers. Written by wildlife veterinarians with many years in the field, they not only provide excellent background on the topic of chemical immobilization, but tables containing drug combinations and dosing recommendations for dozens of wildlife species that are commonly encountered in the field.

The first is Chemical Immobilization of Wild and Exotic Animals, authored by Leon Nielsen and published by Iowa State University Press in 1999; the second, Handbook of Wildlife Chemical Immobilization by Jon Arnemo and Terry Kreeger. These two references are widely available and sufficiently comprehensive that even in the event that truly rare species are encountered, the veterinarian should have sufficient information therein to extrapolate safe drug dosing protocols.