Differences in Urinary Biomarkers as Potential Risk Factors for Ammonium Urate Stone Formation in Bottlenose Dolphins (Tursiops truncatus)
Ammonium urate (NH4U) nephrolithiasis has been associated with morbidity in bottlenose dolphins (Tursiops truncatus) under human care at the U.S. Navy Marine Mammal Program (MMP).1 While population prevalence of nephrolithiasis was reported as approximately 35% at the MMP, no free-ranging bottlenose dolphins from Sarasota Bay have demonstrated sonographic evidence of disease.2 This study compared urinary biochemical, acid-base, and physicochemical parameters between pre-prandial and post-prandial MMP dolphins and post-prandial Sarasota Bay dolphins in order to better characterize the difference in stone prevalence between these two populations. Furthermore, the acid-base content of common prey species in both populations was evaluated. Of the 12 MMP dolphins included in this study, 7 had sonographic evidence of nephrolithiasis, while none (n = 15) of the Sarasota Bay dolphins had evidence of disease on unilateral examination. MMP dolphins were significantly older (median age 29 years vs. 16 years, p < 0.05) and had significantly higher urinary pH, phosphorus, titratable acidity (TA), and net acid excretion (NAE), as well as significantly higher post-prandial ammonium (p < 0.05). Free-ranging dolphins had significantly higher citrate and saturation indices of uric acid, calcium oxalate, and ammonium urate (p < 0.05). Commercially available, non-typical prey fish fed to MMP dolphins demonstrated a higher acid-ash content compared to typical fish types consumed by wild dolphins.3-6 The differences in urinary biomarkers, as well as acid-ash content of diets between these two populations, suggest a pathophysiological basis for the role of fish types, as well as feeding strategies, on the risk of NH4U stone formation in MMP dolphins.
The authors would like to thank the trainers, research assistants, veterinary technicians, and veterinarians at the Navy Marine Mammal Program, including the U.S. Army Animal Care Specialists, for their assistance with sample collection. The authors would also like to thank the staff and volunteer participants in the Sarasota Bay health assessments for wild dolphin sample collection and processing. Funding for this project was provided by Office of Naval Research Award N000141512327, and the research protocol was approved by the Navy Marine Mammal Program IACUC and the Navy Bureau of Medicine and Surgery.
* Presenting author
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