Abstract

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.