Probable Cause Corrective Measures Low average incubation temperature Follow recommended incubation temperatures. Poor ventilation Increase ventilation rate in incubator and/or room, but avoid drafts. Navel infection (Omphalitis) Clean and disinfect incubator and hatching units between settings of eggs. Maintain dry hatching trays. Properly store and fumigate eggs.

Still Air Incubators

Still air incubators are the most basic form of incubator. A still air incubator is basically an insulated box consisting of:-

1. A Heating element
2. A Thermostat or temperature controller to control temperature Egg tray
3. A thermometer to measure the air temperature
4. A tray for water
5. Some machines may have an hygrometer for humidity measurement
6. Some machines may have turning mechanism for automatic turning of eggs

The air inside a still air incubator is circulated by convection. As the air is heated it expands and rises to the top of the incubator. The amount of airflow achieved in a still air machine is therefore determined by the ratio of air temperature inside the box to outside. The lower the air temperature outside the box the greater the airflow inside. To achieve good air circulation, air inlets are usually positioned in the base and top of the incubator. Inside a still air incubator, the warm air moves towards the top so different temperatures will be recorded at different levels. It is therefore important that a still air incubator is kept on a level surface and that eggs are
all of similar size.

Forced Draft Incubator

The forced draft machine was developed to overcome temperature gradient problems throughout the incubator. In a forced draft incubator a fan is used to circulate the air, which gives a uniform temperature throughout the machine. The air temperature surrounding the egg is therefore constant and positioning of the thermometer and temperature sensor are less critical. Eggs, too, can be of differing size and set in trays at different levels.

Using a forced draft incubator also allows the use of a Wet Bulb Thermometer (explained in more detail later), which can be used for the accurate reading of humidity. It is of more importance to control humidity in a forced air machine to prevent the higher airflow drying the eggs.