Date of Award


Document Type


Degree Name

Doctor of Philosophy (PhD)

Legacy Department

Animal and Veterinary Sciences

Committee Chair/Advisor

Maurice, Denzil V

Committee Member

Hall , Michelle A

Committee Member

Layfield , Kevin D


The aim of this dissertation was to investigate the effects of manipulating the incubation temperature during late broiler embryogenesis on hatchability, chick quality, secondary sex ratio, and grow out performance under field conditions. Four experiments were conducted at a commercial hatchery and two setters of 42,240 eggs each were used; one served as control and the other as test with the same physical environment as the control except that thermal stimulation of 0.5o C and 1o C above the optimal incubation temperature were used, in the first two experiments and last two experiments respectively, for 2 h/d from 18 to 20 days of incubation (DI). Temperatures were verified by the use of data loggers in each unit. The experiments were replicated over time with four or five replicates and about 20,000 chicks from each group placed in the field weekly. Chicks were sampled at hatch and at one week of age and body weight, feed conversion and mortality measured at market age. Moisture loss, embryo temperature, hatchability, chick weight, chick rectal temperature, chick quality, and residual yolk sac weight were measured and sex determined after dissection. Thermal stimulation of 0.5o C increased the proportion of hatched males by 3.5% (p= 0.013) and 2.2% (p= 0.008) respectively in the first two experiments and in experiment 2 evaluation at 7 days of age showed that the difference in secondary sex ratio was still evident with 2.8% (p



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