Effects of Particle Size on In Vitro Digestion of Japanese Macaques’ Foods

抄録

Chewing reduces digesta particle size and is critical for herbivores to obtain nutrients. Previous studies of domestic animals have shown that reducing digesta particle size leads to more efficient digestion. Accordingly, the expectation is that increased digesta particle size should be a sign of an animal consuming challenging food and experiencing compromised nutritional intake. However, for some primates that are dietary generalists, digesta particle size has been shown to increase when consuming preferred foods, which raises doubts about the role of chewing in digesting such foods. This uncertainty makes it difficult to understand the connection between diet, chewing, and digestion through digesta particle size in dietary generalists. In this study, using five typical food items from the Japanese macaque diet, we conducted in vitro digestibility and fermentation assays to explore the effects of particle size on enzymatic and microbial digestion. For the fermentation assays, we used feces from captive Japanese macaques as inoculum. We found that particle size has a stronger influence on the digestibility of seeds and mature leaves compared to young leaves and pulp. The influence of particle size on fermentation speed was stronger in pulp and seeds compared to that in leaves. Physical structure, texture, digestion barriers, and soluble components may play important roles in such differences. These results support the hypothesis that reducing food particle size is less important for consuming fruits than for consuming leaves. The limited effects of particle size on digesting fruits suggest that they are cost-effective in food processing and chewing, which provides new insight into the preference of fruit in the diet of generalist primates.