EST is a reflection of the embryo’s temperature and can therefore be used in practice to determine the correct machine temperature required for a batch of eggs.
When ESTs in a batch of eggs vary, development of some embryos is impeded while it is increased for others. The consequences of variation in development within an incubator are a longer hatch window and reduced chick quality and uniformity, because some embryos are incubated at suboptimal temperatures. Uniform and correct ESTs are vital to ensure optimal hatch results and chick quality.
Egg size and EST
Egg size is one of the egg’s characteristics that influence EST. During the second half of incubation, embryonic growth and heat production increase compared to the first part of incubation. From day 15 of incubation onwards, embryos in large eggs have a higher growth rate and a corresponding higher heat production than embryos in small eggs.
In addition, large eggs have a relatively small surface area and a relatively large content compared to small eggs. This makes a large egg less capable of removing heat than a small egg. As a consequence, the EST in large eggs increases more than in small eggs when they are incubated at the same environmental temperature and the embryo inside a large egg is at risk of overheating.
Egg size variation within a flock
Variation in egg size in a batch of eggs in one incubator can occur because of the natural variation in, for example, body weight of the hens within a breeder flock. As a consequence, the eggs that are laid vary in size as well.
When eggs with a large variation in size are set in the same incubator, the incubator design influences the variation in EST. Correct incubator design is crucial to maintain all ESTs within the optimal range of 99.5-100.5ºF, despite differences in egg size. The conditions within an incubator should allow optimal heat exchange between the eggs and the environment at all locations in the incubator. A uniform air flow is required to ensure an equal air velocity through the incubator.
Air velocity plays an important role in allowing an egg to lose surplus heat. High air velocity (> 1 m/s) results in improved heat exchange between an egg and the air and minimizes temperature differences between small and large eggs. A laminar airflow ensures a uniform air velocity throughout the incubator. As a result, all ESTs can be maintained between 99.5 – 100.5ºF and optimal conditions can be provided for eggs of different sizes.