Proboscis monkeys are highly specialized Bornean primates with unique dietary and social requirements that make them extremely challenging to maintain in zoo environments.
Proboscis monkey welfare in captivity represents one of the most challenging cases in zoo management — indeed, most zoological facilities avoid attempting to keep this species due to the extreme difficulty of meeting their needs. Their ruminant-like digestive system requires specific fermentation of particular leaf species, and feeding inappropriate foods causes fatal bloating. Their semi-aquatic behavior requires large water features. Their social complexity involves harem groups and bachelor male groups. These combined requirements mean that even well-intentioned facilities struggle to achieve acceptable welfare outcomes. The welfare consensus for proboscis monkeys is that conservation resources are better directed toward protecting their Bornean habitat than maintaining problematic captive populations.