The effect of clay supplementation on fecal consistency, parasites, and gut microbiome in captive macaques

Abstract

Geophagy, or the consumption of earth materials, is prevalent across primates, including humans. The main drivers of this behavior are unknown. However, often the consumed materials have high amounts of clay, which can absorb water, bind plant secondary compounds, supplement minerals, alter the gut pH, and influence the gut microbiota. As a result, clay supplementation could have a range of potential health applications. Yet, few studies have evaluated the potential benefits or risks of clay consumption. To begin to address this knowledge gap, we describe the effects of daily clay supplementation for one week on fecal consistency, parasite burdens, and gut microbiome composition in 14 healthy captive macaques (Macaca spp.). We trialed two food-grade clay minerals, kaolinite and montmorillonite, using several delivery modes. We found that the monkeys consumed the clay supplements and preferred kaolinite delivered in either peanut butter or bananas. The overall health of the monkeys was minimally affected by clay supplementation, both during the one-week supplementation trial period and for three weeks after. In response to clay supplementation, fecal consistency remained ‘normal’ for 67% of the monkeys; however, 33% developed “clay-like” feces, suggesting that the amount of clay received was too high. Parasite prevalence increased during the treatment phases, potentially due to more frequent sampling, but the composition of the microbiome was mostly unaffected. Clay is known to be a powerful binding agent, but these results suggest that it may not adsorb or affect the microbiome, which antibiotics may do. Overall, our results suggest that clay supplementation does not have short-term negative health effects in healthy captive macaques and should be tested in other primates and humans. We encourage longer trials with additional primate species to 1) determine a safe and effective dose that reduces negative side-effects like constipation, 2) to evaluate the effect of food vehicles, and 3) to determine the effect of clay on other systems and functions.

Supplemental Material: https://tinyurl.com/4nhcfwkv