Impact of a High‐Fiber, Fruitless Diet on the Gut Microbiome, and Health of Captive Orangutans

Diet is a crucial factor in modulating the gut microbiome, and understanding these interactions in captive primates is essential for their health and welfare. This study assessed the impact of the transition to a high‐fiber, low‐sugar diet on the gut microbiome, behavior, and physical health of five captive Bornean orangutans ( Pongo pygmaeus ). We hypothesized that altering dietary patterns would significantly influence gut microbiome diversity and composition, as well as behavioral and physiological indicators. Over 12 weeks, the orangutans were gradually transitioned from a fruit‐rich diet to a high‐fiber, fruitless diet, with progressive dietary changes implemented every 2 weeks. Fecal samples were collected throughout the study, and the microbial diversity and composition were analyzed using 16S rRNA amplicon sequencing. Statistical analyses using linear mixed‐effects models evaluated changes in microbial diversity and composition over time. In parallel, fecal consistency, behavior, and body condition scores were monitored regularly. The results showed significant changes in microbial richness and diversity associated with the dietary transition, with specific taxa, such as the genus Prevotella and the family Ruminococcaceae, increasing in abundance. The microbiome shifts were accompanied by changes in body condition and fecal scores, as well as reduced stress‐related behaviors ( p < 0.05), increased feeding duration ( p < 0.001), and increased social behaviors, including intraspecific interactions ( p < 0.05). This study provides preliminary evidence that a high‐fiber, low‐sugar dietary approach may influence gut microbiome composition and selected behavioral indicators in zoo‐housed orangutans.