Meeting Abstract
At hatching, precocial Pekin ducks rapidly undergo physiological and metabolic changes associated with expression of an endothermic phenotype. Thyroid hormones (TH) are key regulators of avian metabolism and are thought to regulate the development of endothermy. To better understand the role of TH in the Pekin duck’s endothermic developmental trajectory, we characterized systemic O2 consumption (Vo2) and ventilation (frequency and tidal volume) in the thermal neutral zone and during cooling under hypothyroid conditions via administration of the thyroperoxidase inhibitor methimazole (MMI, 87.57 mM/kg) and hyperthyroid conditions via triiodothyronine (T3, 297 µM/kg) supplementation. Animals were dosed on day 24 of a 28-day incubation period and studied on incubation day 25, during external pipping (EP), and 1-day post hatching (DPH). On day 25, there was an increase in Vo2 in the hyperthyroid group compared with the other two groups. During the EP stage, there was a significant effect of thyroid status on Vo2 with hyperthyroid being highest and hypothyroid lowest. By 1DPH, the hyperthyroid and control animals had the same Vo2 response to cooling: a thermal neutral zone followed by an increase in Vo2. The hypothyroid 1DPH animals had a lower resting Vo2 that did not increase to the same extent as the hyperthyroid and control animals during cooling. During EP, hypothyroid animals had lower ventilation frequency and tidal volume than control and hyperthyroid animals. As 1DPH, ventilation frequency of all animals increased during cooling while tidal volume only increased in hyperthyroid and control animals. Our data suggest TH plays an active role in systemic development of endothermic metabolic capacity. In the neonate avian, multiple systems develop in concert to produce an endothermic phenotype, but reduced TH can delay maturation of endothermic capacity in this species.
