Vitamin D and mineral metabolism in the hindgut fermenting Pachyderms: What can happen if we take elephants, rhinoceroses and tapirs out of their natural environment?

Non-infectious diseases appear in both captive and wild pachyderms, metabolic disturbances, however, are only seen in the captive pachyderms (Chapter 2). Captive Asian elephants appear to suffer from hypocalcaemia occasionally and captive black rhinoceroses might suffer from hypophosphataemia and Iron overload disorder (IOD) (Chapter 2). The subject matter of the thesis deals with disturbances in vitamin D, calcium (Ca), phosphorus (P) and iron (Fe) metabolism in captive pachyderms and contains a treatise of personal cases and experiences of veterinary science in practise. The thesis describes how these disbalances in the captive pachyderms might arise, starting with collection of information regarding evolution, ecology, anatomy and physiology (Chapters 1 and 2). Several chapters describe original research (Chapters 3, 4, 5 and 6) that provide more insight to answer specific questions which arose during practice and the literature search into the biology of elephants, rhinoceros and tapirs. The biggest challenge during this search was to collect enough animals/samples for a thorough study. What can happen if you take elephants, rhinoceroses and tapirs out of their natural environment? The research demonstrated that both elephant species (Asian and African) (Chapters 3, 4 and 5) seem unable to endogenously produce sufficient vitamin D3 at latitudes ≥ 52°N (Chapters 3, 4, 5 and 6). Calcium metabolism in Asian elephants might be (partly) depended on vitamin D, at least when dietary Ca levels are low (Chapter 4 and 7), in contrast to their African counterparts (Chapter 4 and 7). The Indian rhinoceros does seem to endogenously produce sufficient vitamin D3 at latitudes of 52°N (Chapter 5) in contrast to the black rhinoceros (Chapters 5 and 6). For rhinoceroses, at least in black rhinoceroses, it seems highly plausible that they are able to endogenously produce cholecalciferol, since the high circulating levels of 25(OH)D3 found in wild black rhinoceroses. It is speculated that this hypovitaminoses D might be associated with hypophosphataemia (Chapter 7), but this will need further investigation for this species. In the black rhinoceros, IOD seems to be associated with the food although this is most likely not the only cause. Also a higher inflammation status which is present in the captive black rhinoceros is positively correlated with %TS levels in serum (Chapter 6) and can possibly lead to IOD (Chapter 6). Next to a higher inflammation status, it has also been speculated that insulin resistance and hypophosphataemia and the incapacity of endogenously producing sufficient vitamin D at higher latitudes could play a role in the development of IOD. The role of stress, reproductive disorders and activity needs to be further investigated (Chapter 7). Malayan tapirs have very low circulating 25(OH)D serum levels and, therefore, seem to resemble horses and might not be dependent as much on endogenous vitamin D3 synthesis but might require adequate levels of vitamin D2 in their diet (Chapter 5). This might be an adaptation to their nocturnal lifestyle (Chapter 2, 7). So, not all pachyderms seem to be able to coop with the current conditions in Europe at latitudes ≥ 52°N (Chapter 7).