The effect of thermal manipulation during embryogenesis on thermotolerance, hatchability and blood parameters of broilers

In order to investigate the effects of different periods of thermal manipulation during embryogenesis on thermotolerance, hatchability and blood parameters of Ross (308) broilers strain, 608 fertile eggs were used in a completely randomized design of 4 treatments with 4 replicates. Experimental groups with different thermal manipulation (for control (0 h), 6, 12 and 18 hours) where incubated at 65% humidity and 39.5°C from 7 to 16 days of incubation. At 7 d of incubation, the infertile and undeveloped eggs were removed after the candling. The result showed that thyroid hormones and facial surface temperature, as metabolism and thermotolerance index, decreased significantly in 6-, 12- and 18-hour-treated groups compared to the control group (P< 0.05). The hatchability was higher in the eggs exposed to 0, 6- and 12-hour thermal manipulation than in the other groups, and a reduction of hatchability was observed in the 18-hour treatment group (P< 0.05). Hatching time increased significantly in the thermal-treated groups (P< 0.05), whereas experimental treatments did not affect body weight, body length, and quality of chickens. Yolk sac percentage was higher in the treated groups than in control (P< 0.05). Increasing the length of thermal manipulation increased the female sex ratio (P< 0.05). The blood concentration of uric acid and total protein significantly decreased in 6-, 12- and 18-hour treatment groups (P< 0.05). In conclusion, based on the results of this study, 6 and 12 hours of thermal manipulation induced thermotolerance without adverse effects on hatchability.