Meeting Abstract
As chickens hatch, there is a rapid change in their physiology and metabolism associated with attaining endothermy. It is thought that thyroid hormones (TH) play a major role regulating the developmental changes at hatching. In birds, TH regulates skeletal muscle growth, which has a direct impact on the chick’s ability to thermoregulate via shivering thermogenesis. To better understand the role of thyroid hormone (TH) in the timing of hatching, the development of thermogenic capacity, and metabolic rate, we manipulated plasma TH levels in chicken embryos beginning at 85% development (day 17 of a 21 day incubation) with either thyroperoxidase inhibitor methimazole (MMI) or supplemental triiodothyronine (T3). After TH manipulation, we characterized O2 consumption and body temperature in the thermal neutral zone and during gradual cooling. Externally pipped embryos, newly hatched 0 day post-hatch (dph), and 1 dph chicks were cooled from 35 to 15°C. Measurements of blood plasma after TH manipulation confirmed both hyperthyroid and hypothyroid conditions. Manipulation of TH altered the timing of hatching, accelerating under hyperthyroid conditions and decelerating with hypothyroid conditions. At rest, there were no differences in resting metabolic rate and body temperature across TH treatment levels. Hyperthyroid EP animals were able to maintain metabolic rate over a wider range of ambient temperatures compared to control and hypothyroid animals. Here, we find that elevating TH levels prior to hatching accelerated hatching and the animal’s thermogenic ability to respond to cooling.
