Variation in Diet and Leafy Browse Offerings Among Colobus Monkeys (<i>Colobus</i> spp.) and Langurs (<i>Trachypithecus</i> spp.) in AZA Facilities

Providing nutritionally balanced diets is a key aspect of successful husbandry and can help support sustainable ex situ populations. This study focuses on the diets of zoo-housed colobus monkeys (Colobus angolensis and C. guereza) and langurs (Trachypithecus cristatus and T. francoisi) across AZA institutions. We utilized survey responses from 34 institutions to (1) document the extent of dietary variation with regard to food categories and macronutrients offered, (2) assess interspecific variation in diets offered, and (3) identify important aspects of browse provisioning among institutions. A total of 95 different food items and 229 common-name browse types were offered across institutions. Leafy greens was the only food category offered at every institution. The proportion of root and non-root vegetables in the diet was highly variable. Nonstructural carbohydrates were the most variable macronutrient, and their concentrations were considerably higher than those food items consumed by free-ranging colobines. Conversely, neutral detergent fiber and acid detergent fiber contents were more consistent across institutions but were notably lower than those of free-ranging colobine food items. There were no significant interspecific differences in diets with regard to food categories or macronutrients offered. There was substantial variation in how frequently browse was offered, how it was regarded across zoos (either as diet, enrichment, or both), and whether or how it was quantified. This study provides context for future studies examining whether and how diet and macronutrient intake impact the behavior, health, and welfare of these populations.