University of Hawaii, Department of Physiology, John A. Burns School of Medicine, Honolulu, HI, USA; Dolphin Quest, San Diego, CA, USA; Dolphin Quest, Waikoloa, HI, USA; Shwetz Veterinary Care, Westlock, AB, Canada; Indianapolis Zoo, Indianapolis, IN, USA; Sea Life Park Hawaii, Waimanalo, HI, USA; Dolphin Quest, Middleburg, VA, USA; Seaworld of San Diego, San Diego, CA, USA; Minnesota Zoological Gardens, Apple Valley, MN, USA; Northwest ZooPath, Snohomish, WA, USA
Abstract
Thyroid gland malfunctions are likely to have detrimental effects on general health, reproduction, and calf survivorship in Tursiops truncatus. For example, congenital goiter has recently been recognized by pathologists as a significant problem in T. truncatus and is believed to be a cause of calf mortality (ref AAZV proceedings 2001, Orlando1).
The first step in treating thyroid diseases in dolphins is to develop a reliable means to diagnose abnormalities. Baseline values that account for the natural variability of thyroid hormone concentrations need to be established to make these assays diagnostically useful for clinical purposes. We performed a standardized study with relatively large sample sizes to determine baseline values for T. truncatus. Our first objective was to examine the effect of non-clinical factors on thyroid hormone concentrations. The main factors we considered were age class, sex, reproductive status, and water temperature.
Our goal was to establish "normal" values for healthy dolphins which we hoped can be used by clinicians to detect primary or secondary thyroid abnormalities. Serum collected from ten facilities comprised a minimum of 40 samples representing at least 8 different individuals for each age and sex class. Over 200 samples from T. truncatus adult females were used to investigate changes in thyroid hormones during pregnancy. All samples were analyzed using radioimmunnoassy techniques for Total T4, Free T4, Total T3, and Free T3.
We found no significant differences in hormone values with respect to water temperature, seasonality or location. Overall means for males and females were similar, but adult females demonstrated greater variability due to an initial rise during early pregnancy and significant decline as gestation progresses. Juveniles of both sexes were found to have significantly higher thyroid values than adults. Of the thyroid hormones investigated, Total T3 demonstrated the least variability, within a standard deviation of 30% relative to the mean for each age/sex class and categorized reproductive state.
Our findings suggest that Total T3 may be the most suitable thyroid hormone for diagnostic applications. Using newly established baseline normal values, we will present individuals with confirmed histologic thyroid abnormalities. These include an individual with an adenocarcinoma and thyroid hormone values for 9 adult females with a diagnosis of calf congenital goiter. Supplementation was found to affect thyroid hormone concentrations, and before and after values are also presented for a thyroxine supplemented animal and several dolphins supplemented with both iodine tablets and seaweed. In conclusion, it appears that thyroid hormone values for these specific cases provide insight into thyroid function in T. truncatus.
References
1. Garner MM, C Shwetz, JC Ramer, JM Rasmussen, K Petrini, DF Cowan, GD Bossart. 2001. Congenital diffuse hyperplastic goiter associated with perinatal mortality in seven captive-born bottlenose dolphins (Tursiops truncatus). Proceedings, American Association of Zoo Veterinarians, Association of Reptile and Amphibian Veterinarians, American Association of Wildlife Veterinarians, National Association of Zoo and Wildlife Veterinarians, Orlando, Florida.