| Summary: | Preheating can increase the efficiency of commercial broiler breeding. A slow increase in temperature can counteract the negative effects of water condensation on the surface of the shell and reduces the thermal shock to the embryos. It is essential to design different preheating profiles because of the variances between breeds in terms of egg construction and the course of embryogenesis, along with the influence of the parental flocks' age on hatching rates. This study aimed to analyze six preheating profiles with different time and temperature patterns (A–F), which were immediately applied before the egg incubation began. These profiles were used for two broiler breeder strains – Hubbard Flex and Ross 308 – for the entire laying cycle divided into six age ranges: 25–30, 31–36, 37–42, 43–48, 49–54, and 55–60wk of life. A total of 7839250 Hubbard Flex and 57167060 Ross 308 eggs were used in the study. The eggs were stored for 4–7d before the preheating profile was applied. Mortality during incubation, hatchability, and the quality of chicks were analyzed. The most favorable results were obtained with profile B – 02 h (25.0 °C):02 h (29.4 °C):02 h (32.2 °C):02 h (35.0 °C):02 h (37.8 °C), while the worst results were obtained with profile C – 03 h (23.9 °C):03 h (25.0 °C):04 h (32.2 °C). These findings indicated that compared to a rapid temperature increase during incubation, multistage slow heating of eggs is more advantageous as it enables achieving better hatchability from apparent fertile eggs and obtaining more first-grade chicks. An analysis of the interaction of different preheating profiles with flock age and breed of parental flock revealed that profile C is not suitable for eggs from older flocks, in particular Ross 308. Deterioration of hatchability of chicks from apparent fertile eggs was also confirmed for flocks over 49wk of life after the application of profile E – 03 h (77 °C):02 h (29.4 °C):02 h (32.2 °C):01 h (35.0 °C):02 h (37.8 °C). Increased early and late mortality of embryos was observed in the case of Hubbard Flex after the use of profile D – 03 h (25.0 °C):02 h (29.4 °C):01 h (32.2 °C):02 h (35.05 °C):02 h (37.8 °C). Based on the obtained results, it can be recommended that profile B can be applied for the entire duration of Ross 308 and Hubbard Flex flock utilization to achieve high egg hatchability and obtain high-quality chicks.
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