Adjusting Our Thinking About Feeding Animals: Fiber as the Metric for Mimicking Natural Diets

Free-ranging animals often ingest markedly different diets than their counterparts under human care, whether companion animals, production animals, or zoo animals. A nutrient with a prominent lack in the diet under human care across species is fiber. Dietary fibers are more difficult to digest than other nutrients and require microbial fermentation, typically resulting in an overall reduction of digestibility and metabolic efficiency. Nevertheless, or therefore, dietary fiber supports health, as it fosters a healthy gut microbiome and limits the risk of obesity and its comorbidities. And due to their lower energy density, high-fiber diets typically increase feeding time, and therefore reduce time available for undesired behaviors. As an adaptation to natural environments replete with high-fiber feeds, humans and animals alike have evolved gustatory preferences for low-fiber, energy-dense feeds. In zoo animal nutrition, the occurrence of both, potentially involuntary feeding of low-fiber diets due to uncritically following feeding traditions, and the deliberate deviation in fiber levels from natural diets, can be documented. Zoo staff appear to transfer their own evolved preference for high-energy feeds to the animals in their care, making zoo animal nutrition a showcase of cultural traditions clashing with biological knowledge. The fiber levels of zoo animal diets can therefore serve as a scale bar for how much zoo management is guided by biological knowledge as opposed to other factors (e.g., anthropomorphism). Increasing fiber levels, possibly to levels observed in the wild, holds great potential for further improvements in the health and behavioral management of zoo animals.