VN May 2022

Vetnuus | May 2022 10 Black rhinos are classified as critically endangered, with population numbers plummeting by 96% between 1970 and 1993. Intensified anti-poaching efforts and strategic translocations have resulted ina slowrecoveryof the species, withnumbers gradually climbing fromonly2600 surviving individuals in the wild in 1993 to over 5600 in 2021. Chemical immobilisation has become an essential tool in the translocation and dehorning of black rhinos, with significant advances in recent years. With the advent of potent opioids, such as etorphine and thiafentanil, the safe immobilisation of large, wild ungulates like the black rhino has become significantly safer for both the animals and the personnel. Before this, animals were physically caught with ropes and a pursuing vehicle, resulting in numerous injuries, fatalities, and failed operations. Black rhinos are good candidates for chemical immobilisation. When darted correctly, inductions can be predictable and quick with the right drugs at optimal doses, and immobilisations can be very stable. Unlike their white rhino counterparts, black rhinos appear more resilient to the respiratory depressive effects of opioids, and cardiovascular functions are generally well-maintained under anaesthesia. Regardless though, their large size and aggressive nature and the rough terrain in which this species often resides canmake chemical immobilisation still somewhat tricky. Black rhinos were one of the first species where etorphine was initially investigated for complete chemical immobilisation. It was combined originally with azaperone, and till today, this remains the combination of choice for many veterinarians. Doses are generally similar to those used in white rhinos, with adult animals requiring 2 - 5mg of etorphinewith 40 – 60mg of azaperone. Doses of up to 200mg azaperone have been reported, although these should be restricted to animals transported after the reversal of immobilisation. Big bulls require the highest doses. Because of the aggressive nature of the animals and their predisposition to excitation during induction, it is always advisable to rather use a higher dose when in doubt regarding the animal's size. Thiafentanil has also beenmixed into the dart to give a 50% etorphine dose and 50% thiafentanil dose in combination with azaperone. It is thought that this provides both the benefit of the quick inductions provided by thiafentanil with the longer immobilisations provided by etorphine. More recently, thiafentanil is being usedon its own as the primary immobilising agent in themixturewith no etorphine in the dart. For quick inductions, thiafentanil can be used in black rhinos in combination with azaperone at similar doses as etorphine. This protocol is particularly useful when darting froma helicopter or in situations where quick inductions are essential because of terrain and the difficulty in recovering immobilised animals. THE CAPTURE AND RESTRAINT OF BLACK RHINO By Dr Liesel Laubscher Dr Cobus Raath and Dr Ben Muller dehorning a black rhino