RESUMEN
This experiment aimed to evaluate the impact of continuous and intermittent thermal stress during early embryogenesis on hatchability, physiological body reaction, ovary weight, and follicle development of quails. A total of 540 eggs were divided into 3 equal groups (3 groups × 6 replicates × 30 eggs). In the first group (control), eggs were incubated at normal incubation conditions (37.5°C and 50-55% relative humidity) from day 0 till hatching. In the second group (continuous thermal stress [CTS]), eggs were daily exposed to 39.5°C and 50 to 55% during the early embryogenesis for 3 successive days (E4-E6) for 3 h (12:00-15:00). In the third group (intermittent thermal stress [ITS]), eggs were daily exposed to 39.5°C and 50 to 55% during the early embryogenesis for 90 min (12:00-13:30) then temperature was returned to 37.5°C for 60 min (13:30-14:30) after that the temperature was raised again for 39.5°C for 90 min (14:30-16:00) daily for 3 successive days (E4-E6). The findings showed that the highest relative water loss form egg (RWL/%) at 6 d of incubation was obtained in the CTS group (P ≤ 0.05). The hatchability rate was significantly (P ≤ 0.05) decreased in the thermal-treated groups compared with the control group. The body surface temperature and cloacal temperature in the CTS and ITS groups significantly (P ≤ 0.001) increased compared with the control group. Chick weight (g) at 5 wk old, total weight gain, daily weight gain were significantly lower (P ≤ 0.05) in the CTS group compared with the control group. Triiodothyronine (T3) hormone concentration and globulin level were significantly (P ≤ 0.05) lower in the CTS and ITS groups compared with the control. The ovarian follicle weights (first, second, third, fourth, and fifth) and the diameter of the large follicle (fifth follicle) were significantly (P ≤ 0.01) decreased by increasing incubation temperature. From these findings, it could be concluded that the hatchability and body weight at sexual maturity for quails produced from eggs exposed to CTS and IST were significantly decreased by 8 and 2.1% as well as 2.98 and 2.1%, respectively, compared with the control group.