Thyroid Hormone Concentrations During Different Reproductive States in Adult Female Bottlenose Dolphins (Tursiops truncatus)
IAAAM Archive
Kristi West1; Shannon Atkinson2; Carol Shwetz3; Jay Sweeney4; Rae Stone5
1Physiology Department, Biomedical Sciences, University of Hawaii, Honolulu, HI; 2Alaska Sea Life Center, Seward, AK; 3Dolphin Lagoon, West Edmonton Mall, Westlock, Alberta; 4Dolphin Quest, San Diego, CA; 5Dolphin Quest, Middleburg, VA


Abnormal thyroid function may present a potential problem to otherwise healthy pregnancies in bottlenose dolphins. In order to diagnostically assess thyroid function in adult females, baseline thyroid hormone concentrations both during different reproductive states and according to stage of pregnancy need to be established. One hundred serum samples from eleven individual adult bottlenose dolphins were analyzed for thyroxine and triiodothyronine concentrations, depending on the volume of available sample. Sixty of these serum samples were analyzed for a complete panel of Total T4, Free T4, Total T3, and Free T3 concentrations. The study animals are housed at Dolphin Quest Hawaii, Dolphin Quest French Polynesia, Dolphin Quest Bermuda, and the Dolphin Lagoon located in Edmonton, Canada.

The study animals were sampled during various reproductive states to develop values for clinical assessment of euthyroid, hyperthyroid, and hypothyroid states in adult female bottlenose dolphins. Hormone concentrations were first compared between pregnant and non-pregnant animals. Both Total T4 and Total T3 were slightly lower in pregnant animals, average Total T4 concentrations were 113.1 ng/ml (± 35.1) in pregnant females, and 125.5 ng/ml (+27.6) in non-pregnant females. Average Total T3 concentrations were 0.95 ng/ml (±0.3) in non-pregnant vs. 1.08 ng/ml (+0.4) in pregnant dolphins. No significant difference was apparent between pregnancy and non-pregnancy for average Free T4 and Free T3 concentrations. Thyroid hormone concentrations in lactating females were considered separately, although many of our pregnant and non-pregnant females were lactating at the time of sample collection.

Matemal thyroid function effects fetal well-being, and in humans expected values are used as a determinant of thyroid disease in pregnant individuals. During a normal human pregnancy, thyroxine varies according to trimesters, with an increase in Total T4 and decrease in Free T4. In bottlenose dolphins, thyroxine concentrations exhibit a different pattern according to gestational stage, as both Total T4 and Free T4 were found to drop considerably as pregnancy progressed. These results indicate the need to further investigate mechanisms concerning thyroid function in dolphins, as our findings show different trends than that of human pregnancy. Our results also provide baseline data for pregnant dolphins, which will allow for clinical assessment of potential thyroid malfunctions. For example, in one bottlenose dolphin individual studied, Total and Free T4 concentrations were extremely low only days before birth, and further investigation is now underway in regards to the death of this calf and what appears to be abnormal maternal thyroxine concentrations.

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Kristi West, MS