A Comparative Study of Intramuscular Alfaxalone- or Ketamine-Based Anesthetic Mixtures in Gray Squirrels Undergoing Gonadectomy: Clinical and Physiologic Findings

SIMPLE SUMMARY: The loss of biodiversity is continuing at an alarming rate worldwide and continuous efforts are required to conserve and protect species and habitats. In 2011, Europe adopted the EU Biodiversity Strategy, aiming to halt the loss of biodiversity and ecosystem services. The increasing number of alien species is one of the leading environmental emergencies. The gray squirrel, introduced to Europe from the USA, is one of the most common and feared invasive species. The introduction of this non-native species is endangering the survival of the smaller native squirrel, called the “common European” or “red” squirrel. The gray squirrel has a devastating impact on native populations of red squirrels as it outcompetes them for food and territory, in addition to carrying diseases. Sterilization is an indirect and humane method for the eradication of gray squirrels; however anesthetic protocols have not yet been standardized. This study describes two anesthetic protocols used to induce chemical immobilization for safe handling, in order to perform the gonadectomy, simultaneously allowing a fast recovery, followed by re-introduction in urban parks. The two anesthetic protocols included a combination of dexmedetomidine and midazolam with either alfaxalone or ketamine. Comparisons of their efficacy and evaluations of their physiologic effects are reported. ABSTRACT: The gray squirrel is one of the most common invasive species in Europe, whose presence is dangerous for the survival of the European red squirrel. To cope with this biological invasion and to safeguard biodiversity, the LIFE+U-SAVEREDS project aims to protect the red squirrel, by limiting the growth of the current population of gray squirrels and simultaneously promoting their eradication with surgical sterilization. This study compares two different anesthetic protocols, including dexmedetomidine (40 µg/kg) and midazolam (0.3 mg/kg) associated with ketamine (15 mg/kg; n = 25 squirrels) or alfaxalone (5 mg/kg; n = 22 squirrels). A blinded investigator evaluated the quality and onset of sedation, intraoperative anesthesia, and recovery, as well as the physiologic parameters for each animal. Alfaxalone provided a good quality of anesthesia with limited cardiovascular effects (p < 0.05) and good intraoperative myorelaxation. Ketamine induced complete relaxation in a shorter time (p < 0.05) and a rapid (p < 0.001) and excellent (p < 0.05) recovery. Despite the overall superiority of ketamine, alfaxalone appeared to be an adequate alternative anesthetic drug that can be administered without requiring intravascular access. It should be rapidly metabolized and excreted; however, it requires the combination of longer acting sedatives/myorelaxants to prevent a poor recovery quality.