Mineral acquisition of Japanese macaques: Contents in the foods, digestibility, and sodium-provisioning experiment

Minerals provide micronutrients that function in various ways in the body, and they are necessary for the survival of animals. In this study, we first compared the mineral content of foods of wild Japanese macaques in lowland Yakushima with that of monkey chow used for many years to feed captive macaques and specifically formulated to obtain good health in captive macaques (National Research Council [NRC] recommendations). Second, we clarified the mineral balance in captive individuals when feeding them monkey chow to clarify the digestibility/bioavailability of the minerals. Third, we investigated the physiological response when we experimentally increased sodium intake. In the lowland of Yakushima, which is in the vicinity (<800 m) of the coast, animals, fungi, and mature leaves had high sodium contents compared with NRC recommendations. The calcium contents of mature leaves and animals were higher than the NRC recommendations. The overall mineral intake in this population was lower than that in the captive animals for calcium, phosphorus, sodium, and iron, while similar for magnesium and higher in potassium. Patterns in the intake and excretion of minerals indicated that excretion was mostly from urine and not from feces, and apparent digestibility was high for sodium. This tendency was opposite for calcium, magnesium, and phosphorus and intermediate for potassium. A sodium-provisioning experiment showed that fecal aldosterone concentration remained low in both control and sodium-provisioning conditions so the macaques do not need reabsorb sodium in the kidneys. Therefore, sodium content in the monkey chow, which is slightly lower than the NRC recommendation, seemed high enough so that the macaques could avoid the need to reabsorb sodium in the kidneys. We advocate similar studies for other primate populations or species to better understand the role of mineral concentrations on food selection and to identify potential mineral deficiencies.