Medetomidine immobilisation and atipamezole reversal in large estuarine crocodiles (Crocodylus porosus) using metabolically scaled dosages

Background Restraint of large estuarine crocodiles is potentially dangerous. Neuromuscular blockers and other immobilising drugs have been used with variable results. Medetomidine has been reported as a reliable, repeatable and reversible immobilisation agent in small estuarine crocodilians. Methods and Results Two wild and two farmed male animals, between 3.05 and 4.6 m long, were hand‐injected into a triceps muscle with a metabolically scaled medetomidine dosage. Immobilisation occurred within 30 min. At the conclusion of the procedures, 70 min after medetomidine administration, three animals were injected with atipamezole IM into the opposite triceps muscle at a dosage based on body surface area. Reversal occurred within 5 min. The fourth animal was intubated prior to reversal of medetomidine and maintained on isoflurane anaesthesia for a gastrotomy. All animals were monitored closely post recovery and then regularly for at least 1 week. Conclusions Medetomidine at a metabolically scaled dosage delivered IM into the forelimb was effective for immobilising large estuarine crocodiles for at least 40 min. Atipamezole administered at a dosage calculated as a function of surface area effectively reversed this immobilisation.     

Preliminary studies of alfaxalone for intravenous immobilization of juvenile captive estuarine crocodiles (Crocodylus porosus) and Australian freshwater crocodiles (Crocodylus johnstoni) at optimal and selected sub‐optimal thermal zones

ObjectivesTo investigate the character of immobilization given by alfaxalone in juvenile crocodiles at optimal and at suboptimal temperatures.Study designProspective, randomized partial crossover study.AnimalsTwenty captive male estuarine (weight 0.6–2.5 kg) and five captive male freshwater crocodiles (weight 0.2–0.6 kg).MethodsCrocodiles were acclimatized for 24 hours at one of the following environmental temperatures; 32 °C, 27 °C, 22 °C or 17 °C, then received 3 mg kg^?1 intravenous (IV) alfaxalone into the dorsal occipital venous sinus. Duration and quality of immobilization was assessed and heart rate (HR) measured. On a separate occasion each crocodile was immobilized at one other environmental temperature.ResultsAlfaxalone, 3 mg kg^?1 IV, produced immobilization for 55 (range 15–100 minutes in estuarine, and 20 (range 20–25) minutes in freshwater crocodiles at 32 °C. There was no significant difference overall in immobilization times between temperatures, other than that, in estuarine crocodiles, duration was shorter at 32 °C than 22 °C. The character of immobilization was unpredictable, with animals recovering without warning, or having extended recoveries requiring assisted ventilation. Assisted ventilation was necessary mainly at the lower temperatures. Median HR in all temperature treatments decreased within 5 minutes post–injection, but the change in HR over the duration of immobilization was affected by the temperature, with a progressively smaller range of fall as temperature decreased. At 17 °C, two estuarine crocodiles appeared to re–immobilize after initial recovery, became severely bradycardiac and required ventilation and re–warming.Conclusions and clinical relevanceAlfaxalone IV in small captive estuarine and freshwater crocodiles provides adequate induction of immobilization at various temperatures. However, the unpredictable results following induction mean it is unsuitable for field use and should be restricted to environments where intubation and ventilation are available, where animals can be warmed to optimal temperature, and where access to immersion in water can be restricted for 24 hours.     

The effects of decreased body temperature on the onset,duration and action of medetomidine and its antagonist atipamezole in juvenile farmed estuarine crocodiles (Crocodylus porosus)

ObjectiveTo determine the efficacy of medetomidine for immobilisation of captive juvenile crocodiles over a range of temperatures, and its reversibility with atipamezole.Study designProspective experimental study.AnimalsForty male estuarine crocodiles (body weight 2.0 to 4.8 kg).MethodsEach crocodile was randomly assigned to one of four temperature groups: Group 1:32 °C; Group 2:27 °C; Group 3:22 °C; and Group 4:17 °C (n = 10 for each group). Medetomidine (0.5 mg kg^?1) was administered intramuscularly (IM) into the thoracic limb of all crocodiles. After 50 minutes, all animals from each group received 2.5 mg kg^?1 atipamezole IM in the opposite thoracic limb and time to recovery was documented. Heart and respiratory rates and the degree of immobilisation were monitored every 5 minutes until recovery, and behaviour monitored for 7 subsequent days.ResultsOnset of immobilisation occurred at 15 ± 10 minutes in Group 1, and at 30 ± 10 minutes in Groups 2 and 3. In Group 4, animals were not immobilised. Recovery following atipamezole was 10 ± 5 minutes at all temperatures. One-way analysis of variance (anova) demonstrated a significant difference in induction times between groups (p < 0.01) but not in recovery times following atipamezole administration (p < 0.25). Heart and respiratory rates decreased markedly following medetomidine administration and increased markedly following atipamezole reversal.Conclusions and clinical relevanceMedetomidine administered in the thoracic limb of juvenile captive estuarine crocodiles provides profound sedation or immobilisation at temperatures of 22 °C and above. Atipamezole administered in the contralateral thoracic limb results in consistent reversal of the effects of medetomidine and a return to normal behaviour within 15–20 minutes regardless of temperature. Even though immobilisation is not induced at 17 °C, profound reversible sedation does occur reliably and repeatably.     

Salmonella in captive crocodiles (Crocodylus johnstoni and C. porosus)

The prevalence of salmonellas in captive Crocodylus porosus and C. johnstoni was investigated at 2 Northern Territory crocodile farms. Similar proportions of each species at one farm (20.0 and 27.8% for C. porosus and C. johnstoni, respectively) carried salmonellas, but at the other farm there was a significant difference between the 2 species (81.0 and 5.0%, respectively). Procedures for the slaughter of crocodiles and processing of crocodile flesh for human consumption are outlined and discussed from the viewpoint of minimising salmonella contamination. The prevalence of salmonellas on flesh for human consumption (16.0% of carcases) was higher than that reported for beef and mutton, but lower than that for poultry products (Murrell 1986). Serotypes most often isolated from cloacai and faecal swabs were S. cerro, S. singapore, S. enteritidis and S. arizonae. Of the 10 serotypes isolated from processed carcases, S. singapore was most frequently isolated (33.3% of serotypes identified).     

First evidence of Kunjin strain of West Nile virus associated with saltwater crocodile (Crocodylus porosus) skin lesions

Recently, the Kunjin strain of West Nile virus (WNV_KUN) has been detected using qRT‐PCR in belly skin lesions of farmed juvenile saltwater crocodiles. This follows an established association between similar lesions and West Nile virus in American alligators. The lesions present as cutaneous lymphohistiocytic aggregates in the dermal layers of both species. While these lesion do not create an obvious defect on the live crocodile, upon tanning the lesion area collapses and does not uptake the dye evenly, thus reducing its aesthetic appeal. As a result, skins are being rejected jeopardising the economic viability of the Australian crocodile industry. Over 50 skin lesions have since been confirmed as WNV_KUN‐positive and preliminary evidence of lesion restructuring is presented. Horizontal transmission of WNV_KUN by mosquitoes is well‐established but other transmission routes, such as ingestion and cloacal shedding, need further evaluation. An infection trial is currently underway to ensure WNV_KUN is the causative agent of these skin lesions.     

Immobilization of Norwegian reindeer (Rangifer tarandus tarandus) and Svalbard Reindeer (R. t. platyrhynchus) with medetomidine and medetomidine-ketamine and reversal of immobilization with atipamezole

The sedative action of medetomidine (-ketamine) was studied in 12 captive Norwegian semidomesticated reindeer (NR), including 4 newborn calves, and in 7 free-living Svalbard reindeer (SR). Medetomidine, with or without ketamine, caused effective, reliable immobilization in NR. Doses of 50-200 micrograms/kg medetomidine alone or 30-125 micrograms/kg medetomidine combined with greater than or equal to 300 micrograms/kg ketamine induced complete immobilization, good muscle relaxation and persistent, deep sedation with little respiratory depression in NR; SR required higher doses. Atipamezole successfully antagonized medetomidine (-ketamine) resulting in rapid and persistent reversal of immobilization in all cases (NR and SR). Both medetomidine and atipamezole had wide safety margins and no conspicuous lasting side effects after reversal.