title: Dietary cation-anion difference may explain why ammonium urate nephrolithiasis occurs more frequently in common bottlenose dolphins () under human care than in free-ranging common bottlenose dolphins.
abstract: Ammonium urate nephrolithiasis frequently develops in common bottlenose dolphins () managed under human care but is rare in free-ranging common bottlenose dolphins. In other species, the dietary cation-anion difference (DCAD) can affect ammonium urate urolith formation by increasing proton excretion as ammonium ions. Therefore, differences in diet between the 2 dolphin populations could affect urolith formation, but the DCAD of most species consumed by free-ranging and managed dolphins is unknown. To compare the nutrient composition of diets consumed by free-ranging and managed bottlenose dolphins, samples ( = 5) of the 8 species of fish commonly consumed by free-ranging bottlenose dolphins in Sarasota Bay, FL, and the 7 species of fish and squid commonly fed to managed bottlenose dolphins were analyzed for nutrient content. Metabolizable energy was calculated using Atwater factors; the DCAD was calculated using 4 equations commonly used in people and animals that use different absorption coefficients. The nutrient composition of individual species was used to predict the DCAD of 2 model diets typically fed to managed common bottlenose dolphins and a model diet typically consumed by common bottlenose dolphins in Sarasota Bay. To mimic differences in postmortem handling of fish for the 2 populations of bottlenose dolphins, "free-ranging" samples were immediately frozen at -80°C and minimally thawed before analysis, whereas "managed" samples were frozen for 6 to 9 mo at -18°C and completely thawed. "Free-ranging" species contained more Ca and P and less Na and Cl than "managed" fish and squid species. As a consequence, the DCAD of both model managed dolphin diets obtained using 3 of the 4 equations was much more negative than the DCAD of the model free-ranging bottlenose dolphin diet ( < 0.05). The results imply that managed bottlenose dolphins must excrete more protons in urine than free-ranging bottlenose dolphins, which will promote nephrolith formation. The nutrient composition of the free-ranging bottlenose dolphin diet, determined for the first time here, can be used as a guide for feeding managed bottlenose dolphins, but research in vivo is warranted to determine whether adding more cations to the diet will prevent urolith formation in managed dolphins.
authors.forename: A J
authors.initials: AJ
authors.lastname: Ardente
authors.forename: R S
authors.initials: RS
authors.lastname: Wells
authors.forename: C R
authors.initials: CR
authors.lastname: Smith
authors.forename: M T
authors.initials: MT
authors.lastname: Walsh
authors.forename: E D
authors.initials: ED
authors.lastname: Jensen
authors.forename: T L
authors.initials: TL
authors.lastname: Schmitt
authors.forename: J
authors.initials: J
authors.lastname: Colee
authors.forename: B J
authors.initials: BJ
authors.lastname: Vagt
authors.forename: R C
authors.initials: RC
authors.lastname: Hill
mesh_terms: D064751:Ammonium Compounds / Q000652:urine*; D000821:Animal Feed / Q000032:analysis; D000824:Animal Nutritional Physiological Phenomena; D000818:Animals; D000835:Animals, Wild; D000836:Animals, Zoo; D000838:Anions / Q000378:metabolism*; D050681:Bottle-Nosed Dolphin / Q000502:physiology*; D002412:Cations / Q000378:metabolism*; D004032:Diet / Q000662:veterinary; D004734:Energy Metabolism; D005260:Female; D005399:Fishes; D006801:Humans; D008297:Male; D053040:Nephrolithiasis / Q000652:urine / Q000662:veterinary*; D014527:Uric Acid / Q000652:urine*
chemical_list: D064751:Ammonium Compounds; D000838:Anions; D002412:Cations; D014527:Uric Acid