Temperature in the incubator should be 99.5 degrees F to 100 degrees F (37.5 degrees C). If the temperature deviates more than degree from 100 degrees F, a poor hatch is likely. Temperature should be checked at least twice a day.

Relative humidity should be set at 86 degrees F to 88 degrees F (30 degrees C) wet bulb temperature. Humidity should not fluctuate more than 1 wet bulb degree. If the incubator uses a passive humidity control system, water should be added daily to the water pan or trough to ensure correct humidity levels.

If the humidity in the incubator is too low or too high, the hatch will fail. When humidity is too low during incubation, the air cell will be too large at the time of hatch. The contents of the egg will be too thick and sticky for the chick to turn. The membranes will be too tough to break. The navel will not close properly.

If the humidity in the incubator is too high during incubation, too little water will evaporate from the egg. The air cell will be too small for the chick to reach during the hatching process. The chick will either drown or the chick will be too swollen with water to turn itself within the egg. The yolk sac will also be too large for the navel to completely close. These problems will cause the hatch to fail.

The air cell of the egg should become larger as incubation progresses. Chicken eggs will lose 12 percent to 14 percent of their total weight by evaporation during incubation. The growth of this air cell is a balance between temperature and humidity during the incubation. Racks of eggs can be weighed during incubation to detect problems with humidity and evaporative loss before a hatch is destroyed.

The chick embryo uses oxygen and produces carbon dioxide. This gas exchange is insignificant during the early period of incubation or when a small number of eggs are incubated. However, recommendations of the incubator manufacturer should be followed to assure that adequate oxygen is available to the developing chicks. Near the end of the incubation period, the eggs are nearly filled with the embryo. An incubator filled with eggs contains a large animal mass that requires large amounts of oxygen. Adequate ventilation is needed during the end of the incubation period. Particular attention should be focused on air vent settings, and wet and dry bulb temperatures during the last third of incubation.

Keep a daily record of the incubator environment. This sample record is designed for use with eggs that hatch after 21 days of incubation. Record keeping can be used to detect mal- functions before a disaster develops. Also, records of fertility and embryo deaths alert the hatchery manager to production, storage, or incubator problems so that adjustments can be corrected before major losses occur.

Proper records call attention to deviations that could destroy a producer's profits. A 5 percent loss of hatchability can go unnoticed. However, a 5 percent loss is 100 percent profit, and conditions that cause a 5 percent reduction in hatchability also contribute to health problems in successfully hatched chicks.