Thermal manipulations of turkey embryos: The effect on thermoregulation and development during embryogenesis

Previous studies conducted on meat-type chickens in our laboratory showed that thermal manipulations (TMs) of the embryo during the time window of the hypothalamus-hypophysis-thyroid axis development and maturation significantly reduced the metabolic rates of the embryo and the chicken, improving the posthatch feed conversion rate (FCR). The aim of the present study was to investigate the effect of intermittent TMs during turkey embryogenesis on embryo development. Fertile turkey eggs were divided into three treatments: control; 6H - with TM by elevation of temperature and RH by 1.7 degrees C and 9%, respectively, above the control conditions for 6 h/d, from E10 through E22, i.e., 240 through 552 h of incubation; and 12H - with TM as above, for 12 h/d, during the same time period. From E0 through E10 and from E23 onward all eggs were incubated under control conditions. The embryo growth rate was not negatively affected by TM. During TM eggshell temperature, the embryonic heart rate and oxygen consumption were elevated by the manipulation while the embryos were in their ectothermic phase. However, by the end of the TM period and until hatch (the endothermic phase) these parameters were significantly lower in both TM treatments than in the control, indicating a lower metabolic rate and heat production. The TM embryos hatched approximately 10 h earlier than the controls, without any negative effects on chick body weight or hatchability. Nevertheless, TM treatments resulted in a higher proportion of chicks with unhealed navels. Body temperature at hatch was significantly lower in the TM chicks than in the controls, suggesting lower heat production and metabolic rate, which might affect the energy requirements for posthatch maintenance. It was concluded that TM during turkey embryogenesis might have altered the thermoregulatory set point, and thus lowered the embryo metabolic rate, which might have a long-lasting posthatch effect.