Respiratory Depression in Llamas During Capture and Chemical Immobilization

Chemical immobilization—whether discussing sedation or anesthesia—has become the chief method of capture for large wildlife species. This is because it has proven to be a safer method compared to traps, capture with nets or the mass-capture of herds of animals. In zoos, farms, breeding facilities and some free-ranging situations, chemical immobilization is usually carried out from the ground. In other cases, wild animals may be located and darted from a helicopter. All of the above capture methods however, can cause significant stress and trauma to target animals, potentially giving rise to complications.

In most cases in the field, remote drug delivery systems are used for the purpose of chemical immobilization, usually via a dart gun or blowpipe. Drugs are injected by means of a dart syringe which is fired from the dart gun at a distance. Since dart volume can be a limiting factor, immobilizing drugs must be highly potent and concentrated. They must also have a high therapeutic index and wide safety margin, since animals often cannot be examined and weighed prior to immobilization.

Llamas and Chemical Immobilization

The llama (Llama glama) is a New World or South American camelid (family Camelidae), a group of animals also referenced as lamoids. This particular group includes llamas, alpacas, vicuñas, and guanacos. It is believed that llamas were derived primarily from the latter species. With reference to the delivery of immobilizing agents to llamas, it should be noted that llamas are sufficiently tractable due to their high level of domestication that individuals can often be injected by hand or with a pole syringe.

Like the camels of the Middle East, Africa and Asia, New World camelids are believed to have originated in North America over 40 million years ago. Lamoids subsequently migrated to South America and camels migrated west via the Bering Strait, later becoming extinct in North America.¹ Today, the majority of llamas live in Argentina, Bolivia, Chile, Ecuador, and Peru. Over the last 40 years, South American exporters have been transporting llamas to farmers and breeders around the world, primarily North America, Australia, and Europe.²

Llamas are pseudo-ruminants, with a single stomach divided into three compartments (as opposed to four, like other ruminants). In the field, llamas graze on grasses and plants. On farms, llamas will eat grass or hay. They consume approximately two pounds per 125 pounds of body weight daily in hay or fresh pasture. ³ Llamas also have a very long large intestine which allows them to go for long periods without water.²

Being the largest of the New World camelids, the llama is primarily employed as a pack animal, but it is also used for its fleece, leather and meat. Adult llamas range in height from 5-1/2 feet to 6 feet tall and weigh between 290 to 440 pounds.¹They have short tails and large, tapering ears. Their feet are narrow and padded on the bottom, allowing these animals to comfortably navigate rough mountain terrain.²

Llamas are social animals that do very well living in herds. Females are called “dams” or “hembras,” while males are called “studs” or “machos.” Castrated males are called “geldings.” Llama offspring are called “crias.” Llamas breed in the late summer and fall. Their gestation period is approximately 11 months, after which the female gives birth to one young.³Female llamas will give birth with the other females in the herd gathered around her to protect the cria from predators. Crias are able to walk and suckle within the first hour of life.^1-3 Llamas have an average lifespan of 20 years.

Llamas communicate through a variety of humming noises, and it is said that they can distinguish between different vocalizations. When they recognize danger, llamas will let out a shrill moan to alert members of the herd.³

Risks for Respiratory Depression in the Llama

Despite their mild demeanor, the chemical immobilization of llamas carries the risk of a variety of complications. As mentioned earlier, since llamas are sufficiently domesticated and easily handled, the administration of immobilizing agents may often be accomplished by hand. But even in the case of highly-domesticated animals such as llamas, animals are often highly-stressed by this process and can run long distances before they are immobilized.

In addition, most of the drugs used for immobilization have side effects; they not only cause sedation by influencing the central nervous system, but also impact cardiovascular, respiratory and thermoregulatory functions.⁵ The most commonly-encountered problems during immobilization events include respiratory depression, cardiovascular disturbances, bloat, compromised thermoregulation, hypoxia and capture myopathy.^5-8

Potent opioids are often used for the chemical immobilization of llamas and other wildlife. A chief disadvantage when using these drugs is that they cause clinically significant respiratory depression due to their potent effect on mu-opioid receptors.⁵ Activation of mu-opioid receptors in the respiratory centers of animals depresses neurons that generate the normal respiratory rhythm. At the same time, activation of these receptors activate other receptors in the brain stem, on the aortic arch and carotid bodies, which depresses normal respiratory function.⁶ Other classes of drugs also have the potential to compromise respiratory function (e.g., through causing hypoxia).

Treating Respiratory Depression in the Llama

Several approaches may be used to mitigate opioid-induced respiratory depression in llamas undergoing chemical immobilization. Assisted ventilation and oxygen insufflation can combat hypoxia brought on by some immobilizing agents,⁵ while agents such as opioid antagonists or partial antagonists can be used (It should be noted that the latter two also reduce desirable effects, such as the degree of immobilization, sedation and analgesia). Respiration can also be improved via respiratory stimulants which act on non-opioid receptor systems such as potassium channel blockers, ampakines and serotonin receptor agonists.⁷

Oxygen supplementation is recommended during the immobilization of llamas, and can be combined with a partial opioid reversal agent to better alleviate hypoxia.⁵ Naltrexone may be used to fully reverse opioid-based immobilization after capture, especially if the animal needs to be released back into the field and must be fully alert.

For the reversal of opioids such as diprenorphine, nalorphine or butorphanol, partial opioid antagonists or mixed agonists/antagonists may be used if residual analgesic or sedative effects are required.^6,7 Signs of recovery after naltrexone administration typically consist of increased respiratory depth, followed by ear twitching, eye movement and lifting of the head.⁵

Partial mu-receptor antagonists (e.g., butorphanol) can be used to alleviate respiratory depression caused by strong mu-agonistic immobilization drugs.^5,8 Some of these partial antagonists, however, also reduce the immobilization effects of opioids. Potassium channel blockers such as doxapram may be used to stimulate breathing. Doxapram is widely used as a respiratory stimulant by veterinarians, and has been shown to increase the minute ventilation in large herbivores immobilized with etorphine.⁵

The drug combinations that are now commonly used for chemical immobilization were not always commercially available as pre-mixed solutions, but many of these can now be purchased from compounding pharmacies as highly-concentrated drug formulations. Many of these are species-specific, more reliable and are less likely to bring about respiratory depression in llamas than drugs and combinations used in the past.