Evaluation of season-related dietary changes on the serum profiles of fat-soluble vitamins, mineral, fatty acids, and lipids in the captive greater one-horned rhinoceros (Rhinoceros unicornis)

Circulating concentrations of fat-soluble vitamins A, D, and E, minerals, fatty acids, and lipids were quantified in five captive greater one-horned rhinoceroses (Rhinoceros unicornis) throughout two time periods, during which two diets were offered. Animals were fed mixed-grass hay and concentrate pellets while managed in barns for winter housing (April sampling, winter diet). During the spring and summer, animals were fed the same amount of concentrate pellet but had free access to North American browse and grasses instead of dried forage (November sampling, summer diet). Levels of 25-hydroxyvitamin D and α-tocopherol were statistically higher in summer diet samples than in winter diet samples. Retinol was not statistically different between seasons, and β-carotene concentrations were undetectable at both time periods. Cholesterol, triglycerides, and non-esterified fatty acids were all significantly elevated following access to unlimited fresh forages in summer. Serum electrolytes were not different between the two time periods but differences in circulating minerals were noted (cobalt, inorganic iodine, and magnesium elevated in winter diet samples; selenium and zinc elevated in summer diet). Access to non-native fresh green forages resulted in improvement of several nutritional parameters in greater one-horned rhinoceroses, implying a benefit when fresh browse and access to grass is provided.