Proboscis monkeys are highly specialized Bornean primates with complex digestive biology. Their welfare in captivity requires exceptional expertise and has historically been very challenging.
Proboscis monkey captive welfare represents perhaps the most challenging case in primate keeping. Their highly specialized fermentative digestive system is so sensitive that dietary errors cause rapid, fatal complications. The narrow range of acceptable leaf species, the prohibition on sugary foods, and the difficulty of replicating their complex arboreal waterside habitat make welfare provision extremely difficult. Historical mortality rates in zoos have been very high, raising serious questions about whether captive management of this species is ethically justifiable outside exceptional circumstances. The few facilities that have achieved success — Singapore Zoo being most notable — have invested enormous resources in specialist husbandry. Conservation value must be weighed honestly against welfare costs when evaluating whether proboscis monkey captive programs are defensible.