UROLITHIASIS IN FREE-RANGING AND CAPTIVE OTTERS (LUTRA LUTRA AND AONYX CINEREA) IN EUROPE.

Between 1996 and 1998, 477 dead otters from different Central European countries were examined for urolithiasis, including 449 free-ranging Eurasian otters (Lutra lutra) as well as 17 Eurasian otters and 11 Asian small-clawed otters (Aonyx cinerea) from captivity. In the free-ranging specimens, uroliths (sand or stones) were found in 105 animals (23.4%), with no significant difference (P = 0.77) between the sexes. Uroliths were not present in any juveniles (n = 26) and urolithiasis was not considered the main cause of death in any individual. In captive specimens, uroliths were found in 11 out of 17 Eurasian otters (64.7%; four males and seven females), and in 3 out of 11 Asian small-clawed otters (27.3%). Histology could not find any signs of inflammation in examined kidneys (n = 179) or urinary bladders (n = 66). Analyzed stones of free-ranging and captive Eurasian otters were composed mainly of ammonium acid urate. The stones of three captive Asian small-clawed otters consisted mainly of calcium oxalate. The difference in prevalence of uroliths between free-ranging and captive Eurasian otters was significant (P < 0.001). Nevertheless, the prevalence in free-ranging specimens of this study is higher than reported before. Differences between various habitats, environmental changes, and genetic predisposition all represent potential hypothetical explanations for these findings.