BENIGN OSSEOUS PROLIFERATIONS OF THE VENTRAL MANDIBLE IN TWO MALAYAN TAPIRS () AND AN OKAPI ().

Three cases of benign ossifying proliferations of the ventral mandible were diagnosed in a 22-month-old female Malayan tapir (), a 12-year-old male Malayan tapir, and a 19-month-old male okapi () at the Denver Zoo Conservation Alliance. The cases each presented with a firm, nonpainful mandibular swelling that would wax and wane in size and were minimally progressive radiographically. Positive reinforcement training, which included scratch down and station standing techniques, was used to obtain serial radiographs. Radiographs revealed mild periosteal proliferation ventral to cheek teeth with no tooth root involvement. A biopsy of the juvenile tapir's mandibular swelling confirmed benign ossifying exostosis. The other two animals did not have biopsies performed and their diagnoses were presumed to be the same as the juvenile tapir's due to similar radiographic findings. The clinical appearance of these lesions can resemble malignant diseases such as osteomyelitis, tumors, or dental maleruptions of ungulates. However, the lesions in the juvenile okapi and female Malayan tapir were found to be unrelated to adult tooth eruption, and the male Malayan tapir was an adult with complete permanent dentition. The mandibular swellings persist in both the okapi and adult tapir cases, respectively, four and two years after identification of each. No further histopathology has been performed in the three cases and the juvenile tapir was lost to follow-up. To the authors' knowledge, this is the first report of ossifying exostosis in a Malayan tapir and suspect diagnosis in an okapi. Benign ossifying exostosis should be a differential diagnosis for facial swellings in ungulates and further investigation including histopathology and long-term follow-up is warranted.