Suspected Moxidectin Toxicosis in Three Species of Hoofstock at a Semi-Free Range Zoological Park
Moxidectin is a commonly used anti-parasitic in hoofstock that is distributed throughout the body and significantly lipophilic. It is labeled for use in cattle by oral, topical, and subcutaneous routes.3 In semi-free ranging conditions, many antiparasitics are administered intramuscularly via dart due to an inability to administer to an individual by other routes without anesthesia. During 2015–2016, three animals including a roan antelope (Hippotragus equinus), sable antelope (Hippotragus niger), and Arabian oryx (Oryx leucoryx) darted with moxidectin developed clinical signs consistent with toxicosis. The primary sign in all three cases was severe neurologic depression. Based on recommendations in canine cases,1-2,4 animals were treated with intravenous lipid therapy and supportive care while diagnostic testing was pending. All three initially improved prior to succumbing to secondary problems associated with prolonged recumbency. Moxidectin has been administered via dart on 73 occasions in seven different species at Fossil Rim during the past 3 yr, with only the above three cases showing clinical signs of toxicosis. Two potential causes in these cases include: poor body condition leading to excessive unbound drug in the bloodstream or a genetic defect similar to some herding dog breeds.2 Given that cases were seen in three different species at an overall low incidence within a given species, a genetic defect is considered unlikely. The animals affected did have significantly lower body condition scoring than their conspecifics, and it is considered likely that this predisposed these animals to toxicosis. Therefore, use caution when administering moxidectin via dart in animals in poor body condition.
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