The Effect of Thermal Conditioning on Thyroid Hormones, Hatchability and Embrionic Mortality of Broilers during the Incubation Period

The aim of this study was to examine the effect of thermal conditioning on the embryonic mortality, on the time of embryonic mortality, as well as to examine the effect of this temperature regime on hatching and on thyroid gland hormone levels. 400 fertile eggs, randomly divided into two groups with two repetitions, were used in this research. The control group was exposed to the standard temperature (37.8°C) through the whole embryonic development. The second group was incubated under the standard conditions as the control group, up to 15^th day of embryonic development. During 16^th, 17^th and 18^th day of embryonic development, the incubation temperature was increased to 39°C for 3 hours. From 19^th day up to the end of the incubation period the conditions of incubation were identical to those of the control group. Results of this study show that the applied treatment leads to an increase of concentration of free T3 hormone on the day 19 of embryonic development, as opposed to a decrease of free T4 hormone in the embryo’s blood compared to the control group. The percentage of hatchability was 82.2% in the control group and 83.3% in the second group. The result shows that this way of thermal manipulation did not affect the embryonic mortality, which was 9.5% in the control group and 8.9% in the experimental group. It can be concluded that in this manner thermal conditioning may manifest the positive effect on the thyroid gland hormone levels without increasing embryonic mortality or disturbing the hatching percentage.