Manipulating plasma thyroid hormone levels at hatching alters development of endothermy and ventilation in Pekin duck (Anas platyrhynchos domestics)

摘要

At hatching in precocial birds, there are rapid physiological and metabolic phenotypic changes associated with attaining endothermy. During the transition to ex ovo life, thyroid hormone levels naturally increase, peaking at hatching, and then decline. To better understand the role of the natural increase in thyroid hormone at hatching in regulating the developmental trajectory of the Pekin duck's endothermic phenotype, we examined development of O-2 consumption ((O2)) and ventilation (frequency, tidal volume and minute ventilation) while inhibiting the developmental increase in thyroid hormones that occurs at hatching via administration of the thyroid-peroxidase inhibitor methimazole (MMI) or accelerating the developmental increase via triiodothyronine (T-3) supplementation. Animals were dosed only 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 (O2) in the hyperthyroid treatment compared with the other two treatments. During the EP stage, there was a significant effect of thyroid status on (O2), with hyperthyroid (O2) being highest and hypothyroid (O2) the lowest. By 1 dph, the supplemented T-3 and control animals had similar (O2) responses to cooling with comparable thermal neutral zones followed by increased (O2). Hypothyroid 1 dph hatchlings had a lower resting (O2) that did not increase to the same extent as the supplemented T-3 and control animals during cooling. During EP, inhibiting the rise in T-3 resulted in embryos with lower ventilation frequency and tidal volume than control and supplemented T-3 embryos. At 1 dph, ventilation frequency of all animals increased during cooling, but tidal volume only increased in supplemented T-3 and control hatchlings. Our data support the role of the late incubation increase in T-3 in regulating the systemic development of endothermic metabolic capacity and associated control of ventilation occurring at hatching of the Pekin duck.