Wild Tiger Health Project
Created by Dr John C M Lewis

Other drug combinations have been used in captive tigers but have not been evaluated in free-ranging individuals. Some of these require an impractically high volume of drugs for field use or rely on component drugs given separately. They include:

• Ketamine, dexmedetomidine and midazolam (Clark-Price et al, 2015)
• Ketamine, medetomidine and midazolam (Curro et al, 2004; Ramsay, 2014)
• Ketamine, xylazine and midazolam (Curro et al, 2004)
• Dexmedetomidine and Zoletil (Lewis, pers. experience)
• Dexmedetomidine and ketamine (Clark-Price et al, 2015; Di Cesare et al, 2020)
• Detomidine and Zoletil (Larricchuta et al, 2015)
• Zoletil and xylazine (Mercado et al, 2020)

Calculating drug doses and volumes
Volume of drug to be administered (in ml) =
Body weight (in kgs) x dose rate (mgs per kg) ÷ Drug concentration (mg per ml)

Example:

• 120 kg tiger to be anaesthetised with 4mg / kg Zoletil
• Body weight x dose rate = 480 mg
• Drug concentration at 100mg per ml
• Volume needed in mls = 480 ÷ 100  = 4.8 mls

These calculations are always better done with a calculator or on paper to be certain of accuracy!!!

The dose rates given are only guidelines. Variations in response to these standard dose rates will be seen in individual animals for a variety of reasons – some unavoidable or unpredictable and others due to human error. It is likely that adjustments to the suggested dose rates will have to be made in the light of local experience. Where possible, it is prudent to use anaesthetic drugs with which the operator is familiar and in which they have confidence. Generally, slight over-doses are better than under-doses as the latter may lead to very long and difficult inductions and situations that may be dangerous to staff. Additionally, when animals are under-dosed, it may be necessary administer more anesthetic before the animal can be handled, resulting in ultimately higher doses and slow recoveries. The safety of personnel must be a high priority when anaesthetising any tiger and it is the responsibility of the anaesthetist to ensure effective and safe immobilization.

As a general rule animals that are moribund or severely ill from their injuries, or have spent prolonged periods of time in a snare or cage, will need lower doses of anaesthetic drugs. Depending on the severity of illness, reduce the normal dose by 20-50%.

Injecting / Darting: By far the best way to inject anaesthetic drugs is by careful hand-injection with syringe and needle into an appropriate muscle. However, this is inappropriate for all but the smallest tigers. Small  individuals can be restrained using a suitable net and then hand injected, but most tigers will require remote injection techniques. Although at close range a lightweight dart projected using a blowpipe can suffice (and is less traumatic than the gas powered systems.) the operator needs to be relatively close to the animal which can cause unnecessary stress and creates unnecessary danger. In the vast majority of cases it will be necessary to use gas-powered dart projection systems such as those made by Daninject,  Distinject, Telinject or Pneu-Dart, or 0.22 blank powered dart projectors such as those made by Paxarms, Pneu-Dart or Cap-Chur Equipment.

The correct preparation and use of darts are best learnt in practical hands-on training from an experienced person rather than from a manual. Anaesthetic drugs should be handled and loaded into darts away from other people, but with assistance available nearby in case of accidents. Excessive trauma from darting is to be avoided not only for humane reasons, but also because bruising will delay uptake of anaesthetic drugs from the darting site. Unnecessary bruising can arise from using needles that are too thick or too long and from darts fired at excessive speeds. Darts projected at excessive speeds are also more likely to bounce out or break upon impact, resulting in partial or no injection.

An excellent review of dart guns, darts and darting techniques can be found in Kreeger & Arnemo 2018, pp 54-78.

If resources allow, it is wise to prepare two or three darts before attempting to dart a tiger. If the first dart misses its target a second dart can be fired with minimal delay. 

Many anaesthetic drugs (and particularly medetomidine) are lipophillic (literally “fat-loving”) which means that they will preferentially stay in fatty tissue. Therefore, if a dart injects its contents into subcutaneous fat the drug will tend to stay there, delaying its absorption into the blood stream and therefore its anaesthetic effect. Slow and sometimes incomplete inductions may result. It follows that a sufficiently long dart needle should be always chosen to avoid subcutaneous injections. In animals that are not restrained by snares etc it is advisable to use a barbed needle to avoid the dart either bouncing out or dropping out too soon. Mark the hub of barbed needles so that the position of the barb can be identified easily for removal. For animals that are restrained by snares, collared needles are adequate.

When darting, aim for the large muscle masses present at the front of the upper hind leg or around the shoulder area. Where at all possible, avoid the head, the chest wall, the abdominal wall, the lower legs and the genital area. Many animals will chew a dart if they can get to it, but fortunately they rarely swallow component parts.     

Preferred darting sites on tiger. Photo: John Lewis

If possible, tigers should be darted when standing still. The loose skin folds present when sitting or lying down can absorb much of a dart’s impact energy, resulting in subcutaneous delivery or even failure to penetrate the skin at all. If an animal is moving when darted, there is a higher risk of dart deflection and inaccurate placement. In the event of a suspected dart failure or partial drug delivery, it is wise to wait a full 15 minutes before giving additional drugs.

Darting tigers located on kills from hides, machans (platforms erected in trees) or from elephant back as practiced in Nepal and southern / north-eastern India is considerably less stressful for the animal compared to being caught in a snare. The use of box-traps is preferable to cage traps for the same reason. Free-ranging tigers have also been successfully darted from helicopters (Russian Far East). It is hoped that in the near future drones will provide a alternative platform from which to dart unrestrained tigers.

Darting animals is not without hazards. Damage to major nerve trunks, blood vessels and bones is only likely in smaller individuals where the dart type, velocity or weight is inappropriate. Dart ricochets are fortunately rare, but the operator must always ensure that no people are within range when firing. When darting unrestrained tigers, the potential for problems is greater and almost entirely beyond the operator’s control. No anaesthetic agent works immediately, and during the time between darting and induction many things can happen. Free-ranging animals can be lost in heavy undergrowth during the partially anaesthetised stage or they may fall into water, down steep inclines, or out of trees in which they have sought refuge.

Darting tigers can also be dangerous for the people involved. Tigers often charge when approached and, if caught in a snare, there is a small chance that they may break free. When dealing with a snared tiger on foot three people should approach to dart. One person should dart the animal, with one person – carrying a flare and, if available, pepper spray – prepared to protect the person with the dart gun should the animal break free from the snare. If necessary, the third person may move around to distract the animal, thereby providing a better angle for a shot. Personnel protection using firearms is also used in some countries, but this should only be done by experienced shooters.

After darting: Without disturbing the animal unnecessarily, an attempt should be made to establish whether the dart has discharged fully. The use of binoculars is recommended. If the dart has not discharged, or not discharged fully, wait 5 minutes and re-assess the status of the dart. Sometimes darts discharge slowly.

After an anaesthetic has been delivered, the animal should be visually monitored from as far away as possible to ensure that the animal is breathing normally and not falling into a life-threatening position. Binoculars can be used to observe the animal and take respiration rates.

It is important to allow sufficient time for an anaesthetic to achieve its full effect. A period of 15 minutes after darting should be allowed before an animal is disturbed irrespective of whether it is down or not – unless an emergency situation such as respiratory arrest develops during this period. Failure to allow such a period may result in partial arousal during the induction period leading to a lighter plane of anaesthesia than would normally be expected with a given anaesthetic dose rate. If no apparent sedation or anaesthesia has been achieved by 15 minutes, consider repeating the darting. Although it is difficult to make hard and fast rules, in the situation of partial but insufficient anaesthesia after 15 minutes, consider giving a further half dose.

Lost darts: An attempt should always be made to retrieve darts that have missed the target.