Humidity control of incubation and weight loss of hatching eggs

The embryonic development is quite adaptive to environmental humidity, between 40%-70%. However, high temperature accompanied with high humidity should be absolutely avoided, because of which will cause embryo death due to suffocation and overheat. Appropriate humidity can help the embryo to be warmed evenly at the early incubation stage, and to give off heat at the late incubation stage. Furthermore, during hatching stage, the chemical reaction between water and carbon dioxide will make the egg shell crisp, which could help the poult pip out. 

During incubation, low humidity cause quick evaporation of the water in the egg, so as to cause excessive dehydration. This result will lead to the sticking between embryo and egg shell if not so serious. A more serious case can lead to embryo death due to the dry chorionic membrane of the allantois which obstructs assimilation of oxygen and exportation of metabolic waste. On the contrary, high humidity will obstruct the evaporation of the water in the egg, which make the residuary water from embryonic development cannot be drained out. This situation will lead to too big stomach of poult and rough navels for the poult to turn itself for pipping, and then suffocate or are drowned to death. To sum up, neither the humidity could be too high, nor it be too low. High temperature accompanied with high humidity is absolutely not allowed.

 During the incubation process, the embryo’s weight loses continually. The lower the humidity is, the more the weight loss is. As for chicken eggs, the best weight loss rate until 20th day is 12%-13%, and with a daily weight loss rate of 0.6%-0.65%. Any weight loss rate out of this range requires a humidity adjustment. There are many factors affecting the weight loss of the hatching eggs. The weight loss may vary for different kind of species, or under different conditions. In term of the same species, under the same conditions, the egg with thicker shell lose less weight than egg with thinner egg shell, and that with less shell surface loses less than that with more egg shell surface. The egg with low ventilating ability loses less weight than that with high ventilating ability. Besides, the size of the ventilation fans, the wind speed, ventilation volume, environmental humidity could affect the weight loss of hatching eggs. Therefore, the best method to set humidity is to check the weight loss rate of the hatching eggs, so as to judge the appropriateness of humidity.

Methods for checking weight loss rate of the hatching eggs

1. Observing air cell.

   This is the most commonly used and the most convenient method during incubation practice. When chicken eggs incubated for 5 days, duck eggs for 7 days and goose eggs for 8 days, the air cell should account for 15% of the total egg area; when chicken eggs incubated for 15 days, duck eggs 18 days, goose eggs 20 days, the air cell accounts for around 25%; when chicken eggs incubated for 18 days, duck eggs 27 days, goose eggs 30 days, the air cell accounts for around 30%.

2. Checking the egg weight

   This method is the comparatively accurate one and it is easy to be mastered by beginner. Each time, weigh the empty egg tray, then set the eggs, and then check the total weight for both the egg tray and the eggs. Finally calculate the weight of the hatching eggs and make a record. When checking the weight loss rate after incubated, subtract the actual eggs weight after incubation from the eggs weight before incubation, then make it divided by the original egg weight, you will get the weight loss rate. Compare it against the standard weight loss rate, you will know whether the humidity is properly set. The optimal daily weight loss rate for chicken eggs is 0.6%-0.65%. Other species may be different in the weight loss rate. When applying this method, it should be kept in mind that the weight loss can vary between cracked eggs and intact eggs, qualified eggs and unqualified eggs, fertile eggs and sterile eggs. Before incubation, strict screening should be made to reject cracked eggs and unqualified eggs. Even during incubation and after each time of weight loss checking, candling is required to identify and reject sterile eggs and dead eggs. Then repeat the work for a new weight loss checking process.