Abstract

Bottlenose dolphins (Tursiops truncatus) managed under human care are reported to develop iron storage disease, or hemochromatosis, but this disease is rarely reported in free-ranging dolphins.^1,2 The prevalence of iron storage disease is not well-described among dolphin management facilities. In one managed population, iron stores were greater in female dolphins and in those of mature adult to geriatric age.¹ The cause of the disease is unknown but may relate to an underlying metabolic imbalance, concurrent chronic hepatitis, and dietary management.^3,4 A definitive diagnosis is rarely made because it requires a liver biopsy; therefore, a presumptive diagnosis is often made based on elevations in serum iron, transferrin saturation, and response to therapeutic phlebotomy.⁵ Serial serum iron concentrations and transferrin saturations, however, are variable and interpretation of clinical signs is subjective. Additionally, concentrations of aminotransferases, ferritin, unsaturated iron binding capacity, total iron binding capacity (TIBC), and inflammatory mediators may lead a clinician to suspect iron storage disease, but inflammation and other disease processes can also affect these biochemical parameters.^1,4,5 We sought, therefore, to determine how facilities screen for and manage iron storage disease in their dolphin populations. This study aimed to identify trends in the diet fed, feeding frequency, or supplementation offered that may be common among facilities with iron storage diseases cases. A survey was distributed via email to 33 facilities managing bottlenose dolphins internationally with a 39% response rate, representing 19 facilities and 285 dolphins under human care. Of these 285 dolphins, 19 (6.7%) from seven facilities were presumed to have iron storage disease. All of these dolphins were over the age of eight years and more likely to be female (58%). The disease screening process varied depending on facility: 87% of facilities measure serum aspartate aminotransferase (AST) and 67% measure gamma-glutamyltransferase (GGT); 100% measure serum iron; and 35–40% measure serum transferrin saturation, ferritin, and TIBC. For each serum parameter, the threshold at which facilities become concerned about iron storage disease varied considerably and trends were more relevant than absolute concentrations. The seven facilities with presumed iron storage disease have treated affected dolphins with therapeutic phlebotomy (83%), fluid therapy (67%), and supplementation (83%). All responding facilities feed herring and capelin of varied proportions, and 44% of facilities feed additional species, including mackerel, sardines, smelt, squid, finger mullet, and sprat in smaller proportions. No commonalities were found between diet and facilities reporting iron storage disease. Dolphins are fed between three and eight times a day, and 83% of facilities reporting suspected iron storage cases feed five to six times daily. All facilities provide a daily multivitamin supplement, and 53% offer additional supplementation, including liver protectants and immune or antioxidant support. One facility provides daily iron supplementation. From this preliminary inquiry, the prevalence of suspected iron storage disease among dolphin management facilities is relatively low, or undiagnosed, and the approach to screening and management varies considerably among facilities. Further discussion on this topic, particularly with respect to screening or diagnostic methods and treatment parameters, is warranted among veterinarians worldwide.

Acknowledgements

We thank the animal health teams of each dolphin management facility that participated in this survey, for taking the time to assist us in this effort.

* Presenting author

Literature cited

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4.  Venn-Watson S, Benham C, Carlin K, DeRienzo D, St. Leger J. 2012. Hemochromatosis and fatty liver disease: Building evidence for insulin resistance in bottlenose dolphins (Tursiops truncatus). Journal of Zoo and Wildlife Medicine. 43(3):S35-S47.

5.  Johnson SP, Venn-Watson SK, Cassle SE, Smith CR, Jensen ED, Ridgway SH. 2009. Use of phlebotomy treatment in Atlantic bottlenose dolphins with iron overload. Journal of the American Veterinary Medical Association. 235(2):194–200.