Proboscis monkeys are endemic to Borneo and among the most difficult primates to maintain in captivity due to their specialized digestive physiology and dietary needs.
Proboscis monkey welfare in captivity is primarily defined by dietary management success. Their ruminant-like digestive physiology makes them extremely sensitive to dietary change, and provision of incorrect food causes fatal disease within days. The very small number of facilities successfully maintaining this species reflects the genuine difficulty of replicating their wild dietary ecology. Where successfully kept, their complex social groups also require careful management. Conservation efforts focusing on wild habitat protection are arguably more welfare-positive than maintaining this species in captivity given the management challenges.