Yoneta H, Dzialowski E M, Burggren W W, Tazawa H
Department of Electrical and Electronic Engineering, Muroran Institute of Technology, Muroran 050-8585, Japan.
Comp Biochem Physiol A Mol Integr Physiol. 2007 Jun;147(2):529-35. doi: 10.1016/j.cbpa.2007.02.001. Epub 2007 Feb 9.
The embryonic modal value of heart rate (MHR) differs between broiler and White Leghorn chickens, but the initial development of cholinergic chronotropic control of embryonic heart rate (HR) does not. Thus, we hypothesized that hatchling MHR should also differ between broiler and White Leghorn strains, while the development of a physiological regulation, such as the endothermic HR response, should not be different between hatchlings of the two strains. To test this, we measured the response of HR and cloaca temperature (Tb) to alteration of ambient temperature (Ta); i.e., 35 degrees C-25 degrees C-35 degrees C, in four groups of hatchlings on Days 0 and 1 post-hatch. Fertile eggs of both strains with similar mass were incubated simultaneously in the same incubator. Eggs of broiler chickens hatched approximately 7 h earlier than White Leghorn chicken eggs. Chick mass at hatching was identical in both strains, but diverged during 2 days after hatching. Tb measured at the initial Ta of 35 degrees C was identical in both strains. MHR at the same Ta was approximately 30 bpm lower in broiler chicks than in White Leghorn chicks, but the difference was reversed to that observed in the embryos. The endothermic HR response was advanced by approximately 1 day in broiler chicks compared with White Leghorn chicks. As a result, eggs of similar mass in both strains produced chicks with similar mass and Tb at hatching, but during 2 days of post-hatch life their masses diverged and regulation of the endothermic HR response developed earlier in broiler than in White Leghorn hatchlings. This physiological heterochrony between strains is most likely due to genetic selection for fast growth in broiler chickens.
肉鸡和白来航鸡胚胎心率的模态值不同，但胚胎心率胆碱能变时性控制的初始发育并无差异。因此，我们推测，肉鸡和白来航鸡品系幼雏的心率模态值也应不同，而诸如产热心率反应等生理调节的发育在两个品系的幼雏之间应无差异。为验证这一点，我们在孵化后第0天和第1天，测量了四组幼雏的心率和泄殖腔温度（Tb）对环境温度（Ta）变化（即35℃-25℃-35℃）的反应。将质量相似的两个品系的种蛋在同一孵化器中同时孵化。肉鸡种蛋比白来航鸡种蛋早约7小时孵化。两个品系幼雏出壳时的体重相同，但出壳后2天体重出现差异。在初始温度35℃时测量的泄殖腔温度在两个品系中相同。在相同温度下，肉鸡幼雏的心率模态值比白来航鸡幼雏低约30次/分钟，但这种差异与胚胎期观察到的情况相反。与白来航鸡幼雏相比，肉鸡幼雏的产热心率反应提前了约1天。结果，两个品系中质量相似的种蛋孵化出的幼雏出壳时体重和泄殖腔温度相似，但在出壳后2天的生活中，它们的体重出现差异，且肉鸡幼雏的产热心率反应调节比白来航鸡幼雏更早发育。两个品系之间的这种生理异时性很可能是由于对肉鸡快速生长的遗传选择所致。
