Practicality of using impala (Aepyceros melampus) as a research model

Abstract

This thesis focus on providing information that furthers our understanding on the practicality of using impala (Aepyceros melampus) as a model for research regarding the effects of immobilisation and general anaesthesia on wildlife generally and wild ungulates specifically. Impala have been used as a research model for around seven decades, but deaths have been reported, especially in experiments where free-ranging impala are placed under captive conditions. There are currently no reports investigating the cause of these deaths. Therefore, the risks involved when using impala in research studies are not entirely known. This paucity in the literature magnifies plausible concerns regarding research ethics and animal welfare that require consideration when using free-ranging animals. This thesis comprises of a series of studies which focus on 1) determining and evaluating the physiological effects of various drug combinations used to immobilise and anaesthetise impala, and 2) determining factors that place free-ranging impala at risk of injury or death when captured and placed into captivity under intensive research conditions. Fifteen adult female impala were enrolled into the 16- week long project. In the first study reported in this thesis, both thiafentanil-medetomidine and etorphine-medetomidine drug combinations successfully immobilised impala, however, despite seemingly normal heart and respiratory rates, all impala were hypoxaemic. Calculated ventilation and oxygenation indices suggested that the hypoxaemia was primarily attributed to right-to-left intrapulmonary shunt of blood. However, other causes of dysfunction in gas exchange such as increased dead space ventilation or ventilation to perfusion mismatch or alterations within the alveolicapillary membrane diffusion, or combinations of all of the above aetiologies for hypoxaemia are plausible. Opioid-induced hypoventilation was not considered a primary cause of the hypoxemia because measured minute volumes were within an appropriate range for medium sized antelope. The second study in this thesis determined if an etorphine-ketamine-medetomidine constant rate infusion was a practical method of maintaining general anaesthesia in impala for up to 120 minutes. However, hypoxaemia, hypercapnia and acidosis were sufficient to require intervention if this protocol is used in the field. The third study evaluated the acid-base status of impala undergoing immobilisation and general anaesthesia using two different drug combinations. In both cases, there was a moderately progressive respiratory acidosis compensated by a marked metabolic response. Both the Henderson- Hasselbalch and the Stewart approaches could explain the acid-base status in the impala. The fourth study determined and discussed the risk factors that resulted in morbidity and mortality in the impala throughout the study period. We found that darting injuries were the highest risk factor that resulted in the most impala deaths during our study. The last study reviewed chemical capture of impala to highlight all the major risks contributing to morbidity and mortality of impala in clinical practice. The greatest risks emanate from the drug and drug delivery factors, where potent opioids (etorphine and thiafentanil) cause profound respiratory compromise, that if left untreated often translates into fatalities. Furthermore, the procedure of darting, an essential tool in game capture, can cause irreparable fractures and other fatal injuries mainly through accidental misplacement of the dart into a long bone, thoracic or peritoneal cavity. Impala are anxious and flighty, and this demeanour (animal related factor) can contribute towards morbidity and mortality rates. The findings of these studies highlight that impala serve as a useful model for improving immobilising and anaesthetic drug protocols, darting techniques or new methods of remote injection in wild antelope. In order to improve animal welfare and the success of similar studies in impala, it is essential that the risks and physiological effects of chemical capture and anaesthesia are well understood before embarking on similar studies.