Commercial Poultry Production and Hatchery Management

HUMIDITY

• During embryonic development, moisture is lost from the egg contents through the shell due to higher incubation temperature.
• Hence, the humidity is to be carefully controlled to prevent unnecessary loss of moisture from the egg.
• The optimum relative humidity in the setter ranges from 50 to 60% or 84 to 86⁰F in wet-bulb reading.
• The humidity is to be adjusted so that the egg loses 0.6% of their original weight every day or 11.5% until the 19^th day.
• When hatching (i.e. in the hatcher), the humidity is increased to 75% (90 to 92 ⁰F in wet bulb) to help the chick break through the shell membrane and shell.
• An excellent method to determine correct humidity is to candle the eggs at various stages of incubation (after 7, 14, and 18 days of incubation) for the size of air cell.
• Necessary humidity adjustments can be made as a result of the candling inspection.
• Closing the vents in the incubators may increase the wet bulb reading and humidity inside the machines, but the developing embryos suffer from poor ventilation.
• Old, dirty, too short, and wrong-sized wicks on wet bulb thermometers can cause erroneous readings.
• It is essential that wicks be kept in the best condition. The wicks should be changed once in a week and replace them with new ones after four to eight washings.
• Inferior wicks tend to give higher readings than are actually present. In other words, the wet bulb tends to act more like the dry bulb.
• This is because the flow of water through the wick has been slowed.
• Therefore, if attempting to maintain an 86⁰F wet bulb reading with faulty wicks, it may actually has an 84⁰F wet bulb environment in the machine.
• The two degrees difference for an entire incubation and hatch period can noticeably reduce hatchability.
• Excessive moisture loss from the eggs during storage before setting can produce the same symptoms that low humidity in the machines produces.
• A sign of low humidity is sticky embryos during pipping and hatching that results in embryos not being able to turn themselves in the shell and complete the act of pipping and detaching themselves from the shell. Low humidity also results in short down on the chicks, malformed, malpositioned, weak, and small chicks.
• High humidity causes several large, soft bodied, mushy chicks that make it through pipping and hatching but are dead in the tray. A bad odor usually accompanies this condition.
• In properly ventilated still-air incubators getting too high humidity is rare.
• The water pan area should be equivalent to one-half the floor surface area or more.
• Increased ventilation during the last few days of incubation and hatching may necessitate the addition of another pan of water or a wet sponge.
• Humidity is maintained by increasing the exposed water surface area.