Modifying the diets of captive proboscis monkeys in a temperate zoo to reduce weight loss and renal disease

In animal husbandry, diets should help in maintaining a healthy body condition, support reproduction, and promote species-specific longevity. It is recommended to feed folivorous primates kept in zoos a high-fiber diet, i.e., leaves, although satisfying such a requirement is challenging in temperate regions because it is difficult to obtain fresh leaves, especially in autumn and winter. As equally important for their appropriate treatment, it is valuable to provide details of clinical reports of medical problems and pathological findings, although such clinical reports are rather limited. Therefore, in foregut-fermenting proboscis monkeys (Nasalis larvatus), we (1) described the individual clinical reports of renal disease and weight loss at the Yokohama Zoological Gardens in Japan, (2) determined the nutritional profile of the diets supplied to these animals because other potential triggers for their renal disease and weight loss could be excluded, (3) modified the diet regimen to minimize weight loss and the development of hypercalcemia and hypophosphatemia, and (4) assessed the effects of such dietary modification by comparing the body weight and the Ca and P concentrations and the Ca/P ratios in the blood before and after diet modification with a comparison of these measurements between zoo and free-ranging individuals. Based on the nutritional profile of the diets, we concluded that the reported cases of renal failure might be caused by consumption of leaves with a Ca/P ratio far above the appropriate level in autumn and winter. Additionally, the dietary modification of minerals and metabolizable energy achieved certain beneficial effects on zoo-kept proboscis monkeys.