Chemical analysis and consistency of faeces produced by captive monkeys (François langurs, Trachypithecus francoisi) fed supplemental fibre.

The effect of additional dietary fibre on the consistency of faeces was studied in a group of four François langurs (Trachypithecus francoisi) kept in Rotterdam Zoo. To increase fibre intake, a diet pellet rich in fibre was offered instead of the usual, commercial primate pellet. This dietary change raised the amounts of hemicellulose and cellulose that were consumed at the expense of non-structural carbohydrates. The experiment had an A1-B-A2 design. Stool quality improved when the high-fibre pellet was fed. The monkeys produced somewhat more faecal dry matter and the faeces contained markedly more non-structural carbohydrates and less crude fibre when the high-fibre pellet was fed. The percentage of water in the faeces was slightly lower when the high-fibre diet was offered. We speculate that the extra fibre was partly fermented and that the breakdown products were recovered in the carbohydrate fraction of faeces. These breakdown products might have a superior water-binding capacity, leading to well-shaped faeces. This study showed that François langurs have the capacity to digest dietary fibre, as has been demonstrated earlier for other species of leaf-eating monkeys.