Iron Overload Disorder (IOD) is a syndrome developed by captive browsing rhinoceroses like black rhinoceroses (Diceros bicornis), in which hemosiderosis develops in vital organs while free iron accumulates in the body, potentially predisposing to various secondary diseases. Captive grazing species like white rhinoceroses (Ceratotherium simum) do not seem to be affected. The authors hypothesized that inflammation and oxidative stress may be implicated in the pathogenesis of IOD in captive black rhinoceroses, making this syndrome a potential common denominator to various diseases described in captivity in this species. In this prospective study, 15 black (BR) and 29 white rhinoceroses (WR) originating from 22 European zoos were blood-sampled and compared for their iron status (serum iron), liver/ muscle biochemical parameters (AST, GGT, cholesterol), inflammatory status (total proteins, protein electrophoresis) and oxidative stress markers (SOD, GPX, dROMs). Results showed higher serum iron and liver enzyme levels in black rhinoceroses (P < 0.01), as well as higher dROMs (P < 0.01) and a trend for higher GPX (P = 0.06) levels. The albumin/globulin ratio was lower in black rhinoceroses (P < 0.05) due to higher α 2-globulin levels (P < 0.001). The present study suggests a higher inflammatory and oxidative profile in captive BR than in WR, possibly in relation to iron status. This could be either a consequence or a cause of iron accumulation. Further investigations are needed to assess the prognostic value of the inflammatory and oxidative markers in captive black rhinoceroses, particularly for evaluating the impact of reduced-iron and antioxidant-supplemented diets.

17Iron Overload Disorder (IOD) is a syndrome developed by captive browsing 18 rhinoceroses like black rhinoceroses (Diceros bicornis) in which hemosiderosis settles in vital 19 organs while free iron accumulates in the body, potentially predisposing to various secondary 20 diseases. Captive grazing species like white rhinoceroses (Ceratotherium simum) do not seem 21 to be affected. The pro-oxidant and pro-inflammatory properties of iron, associated with the 22 poor antioxidant capacities of black rhinoceroses, could enhance high levels of inflammation 23 and oxidative stress leading to rapid ageing and promoting diseases. In this prospective study, 24 15 black (BR) and 29 white rhinoceroses (WR) originating from 22 European zoos were blood-25 sampled and compared for their iron status (serum iron), liver/muscle biochemical parameters 26 (AST, GGT, cholesterol), inflammatory status (total proteins, protein electrophoresis) and 27 oxidative stress markers (SOD, GPX, dROMs). Results showed higher serum iron and liver 28 enzyme levels in black rhinoceroses (P<0.01), as well as higher GPX (P<0.05) and dROM 29 (P<0.01) levels. The albumin/globulin ratio was lower in black rhinoceroses (P<0.05) due to 30 higher  2 -globulin levels (P<0.001). The present study suggests a higher inflammatory and 31 oxidative profile in captive BR than in WR, possibly in relation to iron status. This could be 32 either a consequence or a cause of iron accumulation, potentially explaining rapid ageing and 33 various diseases. Further investigations are needed to assess the prognostic value of the 34 inflammatory and oxidative markers in captive black rhinoceroses, particularly for evaluating 35 the impact of reduced-iron and antioxidant-supplemented diets. 36