Variation in zoo diets, offerings of leafy browse, and body condition scores in Matschie’s tree kangaroos ( <i>Dendrolagus matschiei</i> ) and their associations with gut microbiome composition

Recommended zoo diets for the arboreal folivore, the Matschie's tree kangaroo (<i>Dendrolagus matschiei</i>; TK) were recently found to be much lower in fiber and higher in starch than wild diet items for this species. In contrast to wild animals, zoo-housed TKs are ~30-40% higher in body mass, known to suffer from infections indicating immune dysfunction, and exhibit various reproductive issues. These problems may have ties to gut microbiome dysbiosis related to differences in diet between captive and wild individuals, but to date, the microbiome of TKs has not been explored. This study aimed to (1) quantify the macronutrient intake of zoo-housed TKs and compare the intake of over-conditioned animals to those at ideal body condition, and (2) examine gut microbial communities for any differences associated with TK macronutrient intake, leafy browse offerings, or body condition. Detailed diet intake information (<i>n</i> = 31 individuals at 16 facilities accredited by the Association of Zoos and Aquariums) was collected for approximately 1 week at two different time points (<i>i.e</i>., July-September and January-March). Body condition scores were recorded by primary caregivers or veterinary staff no more than one month from each diet intake week. Fecal samples (<i>n</i> = 57) were collected concurrently during the diet recording weeks. We used 16S rRNA gene amplicon sequencing to examine TK gut microbiota. We found that animals assigned over-conditioned body scores consumed significantly more kilocalories compared to animals assigned an ideal body condition score. These differences were driven primarily by significantly greater crude protein and starch intake in over-conditioned TKs. TKs offered high and intermediate amounts of leafy browse exhibited substantially different fecal microbial communities compared to animals offered low or no browse. Our results indicate that formulation of diets for zoo-housed TKs, similar to other folivores, should closely resemble the macronutrient and caloric values of wild counterparts to encourage ideal body condition and promote gastrointestinal health. Future research should examine the gut microbiota of free-ranging TKs and assess how different species of leafy browse impact TK gut microbiota.