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Thermal manipulations of broiler embryos—The effect on thermoregulation and development during embryogenesis¹

Y. Piestun^*,, O. Halevy and S. Yahav^*,2

^* Institute of Animal Science, the Volcani Center, Bet Dagan 50250, Israel; and Department of Animal Sciences, Faculty of Agriculture, the Hebrew University of Jerusalem, Rehovot 76100, Israel

² Corresponding author: yahavs{at}agri.huji.ac.il

This study aimed to elucidate the effects of thermal manipulations (TM) of broiler embryos, during the development of the thyroid and adrenal axis, on embryo development and metabolism. Cobb eggs were divided into 3 treatments: control, 24H–continuous TM at 39.5°C and 65% RH from embryonic day 7 to 16 inclusive, and 12H–intermittent TM for 12 h/d in the same period. Only the 24H treatment negatively affected embryo growth and development, with lower relative weights of embryo, liver, and pipping muscle. During TM, eggshell temperature, heart rate, and oxygen consumption were elevated as embryos were in their ectothermic phase, but from the end of the TM until hatch, these parameters were significantly lower in both treatments than in the control. Moreover, plasma concentrations of the thyroid hormones were significantly lower in the 2 treatments during and after TM, until hatch. Plasma corticosterone concentration of the TM-treated embryos was significantly lower after the TM but significantly higher at hatch. It was concluded that TM during the development of the thyroid and adrenal axis lowered their functional set point, thus lowering metabolic rate during embryogenesis and at hatch.

Key Words: thermal manipulation • incubation • oxygen consumption • eggshell temperature • embryonic growth

¹ Contribution from the Agricultural Research Organization, the Volcani Center, Bet Dagan, Israel. No. 539-09.