Wounds in Nyala Antelope During Chemical Immobilization
Chemical immobilization events present risks to wildlife regardless of size or species, but these are more pronounced when dealing with larger species such as antelope and other hoofstock in the field. Associated risks include complications such as aspiration, dehydration, hypothermia, hyperthermia, capture myopathy, respiratory depression and/or arrest and cardiac arrest. These complications can come about as the direct result of chemical immobilization, either due to inadvertent overdose, comorbidities or latent sensitivities among individual animals.
The nyala is an antelope that is native to Southern Africa. It is a species of the family Bovidae and genus Tragelaphus and was first described in 1849 by George French Angas.1 The nyala’s coat is a chestnut brown in females and juveniles, but grows a dark brown or grey in mature males. There are two subspecies of nyala: The lowland nyala (Tragelaphus agasi), and the mountain nyala (Tragelaphus buxtoni).
Female and young male nyala have ten or more white stripes on the sides. Both males and females have a white chevron between their eyes and a long, bushy tail a white underside. Only the males have spiral horns; these are yellow-tipped and have one or two twists.
The nyala occupies dense woodlands on the coastal plains and major river valleys of eastern Africa from southern Malawi to Natal and is a cover-dependent browser and grazer.2 Their habitats include lush grasslands next to the cover where these animals spend the day; at night, they emerge to graze during the rainy season. Their habitat requirements are thought to be partly due to the fact that nyala do not have the explosive running ability of many other African antelope. Females and young live in small herds of five or six animals. Male nyala are nonterritorial and occupy overlapping ranges.
Risks for Wounds in Nyala
Wounds incurred during capture events are a complication that may be considered less critical in the context of complications, but these must be seriously considered. Wounds can occur as a result of an animal attempting to flee prior to immobilization, as it loses physical coordination during take-down after darting or, rarely, from the darts themselves.3
Physical injuries are among the most common threats to wild animals. In some cases, animals can incur severe injuries that kill them directly. In other cases, their injuries can affect them in ways that are indirectly fatal (e.g., reducing their ability to find food or to evade predators). Apart from human-related causes, these can come about as a result of many events (e.g., evading predators, fighting for mates or territory, accidents). Even when an animal doesn’t die as a direct or indirect result of an injury, it can be left in a permanently compromised state or with chronic pain.4
When an animal suffers a wound during capture/chemical immobilization, ethical imperatives dictate that those undertaking the required research or wildlife management protocols make every effort to ensure that the animal is promptly treated so that it can make as complete a recovery as is possible.
Antelope vary widely in size, but nearly all antelope are considered to be large hoofstock. Additionally, all antelope are prey animals, and have evolved with instincts and behaviors gauged to help them survive. Consequently, all antelope will attempt to flee when approached in the field. Occasionally, this can result in injuries either before or after a nyala is darted. If the approach by humans is protracted (e.g., a long vehicle or helicopter chase), the risk of complications and injury can be increased manifold. While a wide variety of injuries is possible in such circumstances, more often than not, when these occur, they are usually soft tissue injuries of varying severity.
Antelope have developed a number of methods to deal with predators, the most noteworthy of which is their speed and agility. If an antelope cannot evade its pursuer outright, it may try to hide in areas that are difficult to access. Some species will freeze in place to avoid being noticed, while others may stand their ground and defend themselves with their horns.4
Treatment of Wounds in Nyala
Most injuries connected with capture events are experienced when a nyala is attempting to flee human pursuers,3 and the most common injuries suffered are lacerations. While remote drug delivery via the dart itself is unlikely to result in a serious injury, darting can on occasion result in minor lacerations. Finally, in some cases the animal may need to be immobilized specifically for the treatment of a serious wound it has suffered due to other causes.
The first step in treatment is to clean the wound. In the case of small, shallow lacerations, this can be done by flushing with a commercial povidone-iodine or other scrub solution. Deeper wounds can be flushed with povidone-iodine diluted with saline, and should generally not be sutured to allow for drainage.3 The current literature recommends high volume, high-pressure irrigation unless the tissue is very delicate. The suggested lavage volume is 50 to 100 mL of fluid per centimeter of wound. Low-pressure irrigation is gentle to tissues and does not force bacteria deeper into the wound, but it does not debride as well as high-pressure irrigation, which can be performed with a pressurized fluid bag or a large syringe with an 18-gauge catheter.4
For suturing superficial wounds that have been cleaned, a veterinarian should perform the procedure. If a veterinarian is not immediately available, non-absorbable sutures should be used.
Any nyala receiving a laceration prior to or during an anesthetic event should be given systemic antibiotics to reduce the likelihood of infection. Procaine penicillin G combined with benzathine penicillin G is a common formulation is these instances. Long-acting oxytetracycine is also frequently used to treat hoofstock that have suffered lacerations.5
Considering the inherent risks associated with chemical immobilization, there is no way to guarantee that injuries will not occur in nyala, particularly under field conditions. That said, the drug formulations currently available for immobilizing antelope and other wildlife have been refined to a degree that eliminates much of the risk that existed years ago. With the right drug formulations, proper planning and safety precautions in place, experienced personnel can have the expectation of effective and incident-free chemical immobilization of nyala in the majority of cases.
3Kreeger T., Arnemo, J., Raath, J. Handbook of Wildlife Chemical Immobilization, International Edition, Wildlife Pharmaceuticals, Inc., Fort Collins, CO. (2002).
4vetfolio.com: Remote Injection Systems. https://www.vetfolio.com/learn/article/remote-inj...
5Friend, M., Thomas, N. J. Field Manual of Wildlife Diseases. In: Field Manual of Wildlife Diseases, United States Geological Survey, 361-368.
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