Metabolic bone disease in juvenile zoo-housed black howler monkeys (Alouatta caraya)

Metabolic bone diseases (MBD) can occur in any animal due to insufficient vitamin D, which is essential for calcium absorption and regulation. New World primates have higher requirements for cholecalciferol (D3) than African or Eurasian primates, along with a decreased ability to utilize ergocalciferol (D2), the form associated with plants and fungi. To investigate the prevalence of vitamin D-associated MBD in parent-reared juvenile black howler monkeys (Alouatta caraya) under human care, records were requested from Association of Zoos and Aquariums-accredited institutions housing this species from 1990–2023. Records for 89 juvenile animals were received and screened for MBD, defined by angular limb deformities with diffuse radiographic osteopenia or histopathologic diagnoses. Twenty individuals (22.47%) were diagnosed with MBD. Clinical signs included palpable angular limb deformities (n = 15, 75%), pathologic fractures (n = 8, 40%), juvenile-onset cataracts (n = 8, 40%), and abnormal ambulation (n = 6, 30%). The mean serum concentration of 25-hydroxyvitamin D (calcidiol) in clinically affected juveniles was 91.77 nmol/L (range 8–173 nmol/L), whereas the mean of clinically normal juveniles at time of first testing was 445.13 nmol/L (range 194–697 nmol/L). Almost all cases survived to adulthood (n = 16, 80%) although permanent angular limb deformity was common (n = 11, 64.7%). Recommendations for prevention and management of this condition include monitoring serum calcidiol concentrations, vitamin D3 supplementation starting from infancy, housing animals outdoors where possible, restricting breeding to result in offspring being born during seasons with sufficient access to outdoor ultraviolet B (UVB) radiation, and providing UVB supplementation when natural light is insufficient. Although clinical MBD may be severe; when treated, these animals may maintain a good quality of life.