Maintaining the correct incubation temperature is one of the most critical factors for successful chick development. When discussing temperature control, it is important to distinguish between air temperature — measured by the incubator’s sensors — and eggshell temperature (EST), which more accurately reflects the embryo’s internal temperature. Scientific research has consistently shown that maintaining an EST of 100°F (37.8°C) throughout all stages of embryonic development — differentiation, growth, and maturation — is vital. While embryos can tolerate brief fluctuations without significant harm, consistent deviations can disrupt normal development. Therefore, incubation programs should prioritize EST as the primary control parameter, adjusting air temperature to maintain the optimal eggshell temperature.
During the differentiation and growth phases, temperature uniformity within the incubator is essential for synchronized embryo development and a narrow hatch window. The embryo’s energy primarily comes from the oxidation of yolk lipids, a process dependent on oxygen supplied by the chorioallantoic membrane (CAM). In the early stages, before the CAM is fully developed, the embryo relies on anaerobic glycolysis of carbohydrates — a limited energy source that becomes depleted after the first week. By day 16, as the embryo transitions to the maturation phase, oxygen uptake reaches its maximum potential. If the embryo is overheated, its oxygen requirements rise, forcing it to draw from alternative energy reserves such as glycogen and muscle proteins. This shift can negatively impact hatchability, chick quality, and overall health. The embryo’s maximum oxygen uptake is determined by both CAM vascularization and eggshell conductance, which depends on shell thickness and pore density. Eggs with lower conductance reach oxygen limits sooner, making them more sensitive to high ESTs above 102°F (38.9°C).
Sustained high EST levels can lead to several developmental problems, including reduced organ size, such as smaller hearts, chicks with unhealed navels, swollen bellies, and lower yolk-free body mass. Higher late embryonic mortality is often accompanied by malpositioning, such as head-over-wing positioning. These issues not only affect hatch success but also farm performance, leading to increased post-hatch mortality, poor feed efficiency, and heightened susceptibility to diseases such as ascites. While the effects of high EST are well-documented, the impacts of low EST (below 100°F) remain less understood. Because embryos are poikilothermic, prolonged low temperatures slow development, reducing hatchability if hatching times are not adjusted. Although the exact mechanisms and outcomes are still being studied, short, controlled temperature deviations — slightly above or below 100°F for a few hours — during specific developmental stages may enhance chick robustness, suggesting that careful temperature modulation could be a valuable management strategy.
The biology behind incubation temperature highlights the delicate balance between heat, oxygen, and embryonic metabolism. By understanding and managing EST effectively, hatchery managers can significantly improve chick quality, hatchability, and long-term farm performance.
