The effects of altering incubation temperature on broiler chick hatchability, chick quality, sex ratio, and subsequent performance under field conditions

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 0.5 °C and 1 °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 0.5 °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<0.001) more males in the test group. In experiment 2 hatch residue was examined and the proportion of unhatched male embryos was greater in the control group than in the test group (p= 0.024). Thermal stimulation of 1 °C improved feed conversion by 1.82% or 3.6 points (p= 0.0491) in comparison to the control group. The results demonstrated that low-intensity, short-duration thermal stimulation during late incubation altered secondary sex ratio at hatch and at 7 days in favour of males and had positive long lasting effect on feed conversion. Thermal stimulation up to 1 °C did not have adverse effects on hatching results and post hatch performance under field conditions.