Holding eggs for more than 10 days reduces hatchability. However, chukar and turkey eggs are an exception. Chukar eggs have been stored 3 weeks to 4 weeks without appreciable loss in hatchability.

Relative humidity is the water vapor in the air expressed as a percentage of the greatest amount of water vapor possible at that temperature. The amounts of water vapor that air can contain are different at different temperatures. To measure relative humidity, expensive equipment or a complicated procedure is required. However, the wet bulb temperature is easily measured and is the method usually used to measure humidity in an incubator. Relative humidity is expressed as a percentage while wet bulb temperature is expressed as degrees.

A wet bulb thermometer can be purchased or made from a common dry thermometer. Knowing how to make a wet bulb thermometer helps to understand how it works. A thermometer, a shoelace (approximately a 6- inch long piece) and a short piece of dental floss are needed. First, stick the bulb end of the thermometer about 1 inch into the hollow of the shoelace. Next, tie a piece of dental floss around both the shoelace and thermometer directly above the bulb. This is to keep the shoelace from sliding off. Place the opposite end of the shoelace directly in a pan of water. If the water is the same temperature as the air temperature, the reading on the thermometer is the wet bulb temperature. The temperature reading of the wet bulb will be less than a dry thermometer because evaporation of water cools the thermometer.

However, the reading also will be influenced by the relative humidity of the air. The wet bulb reading is used as an index of relative humidity but is not numerically equal to the relative humidity value. The wet bulb temperature will change at different dry bulb temperatures even as the relative humidity remains constant. So, the appropriate wet bulb temperature that is to be maintained must be known for each dry bulb temperature that occurs during storage.

Relative humidity in the storage room should be approximately 70 percent to 80 percent (wet bulb temperature of 50 degrees F to 60 degrees F). Condensation forms on eggshells exposed to excessive humidity. Condensation on the eggshell can clog pores and, like washing eggs, provides a vehicle for contamination. Suffocation or contamination of the embryo can result. Excessive amounts of water evaporate from the egg if humidity is too low, which also causes embryo death. To increase the humidity, a pan of water can be placed in the storage room. If the incubator temperature is correct, the only factor governing humidity is the surface area of water inside the incubator or storage unit. Avoid drafts during storage that can dry eggs even when humidity levels are within appropriate levels.

Hatchability is best maintained by storing eggs with the small end down in sealed, airtight plastic bags. The bags help keep the eggs clean and prevent moisture loss.