How can you tell if ventilation is poor?

The first thing noticed may be a poor hatch. Lack of proper ventilation can contribute to low hatchability if, after examining numerous dead embryos in the shell, the following conditions are observed:

  1. The majority of embryos reach the 19th or 20th day of incubation.
  2. They are not dehydrated.
  3. They are not malpositioned.
  4. The unabsorbed egg yolks appear to be disease free.
  5. The wet bulb reading usually ran closer to 90oF. rather than 86oF.
  6. The heating element is seldom on during latter stages of incubation.
  7. The dampers are not as open as expected.


Birds, including chickens and quail, turn their eggs during nest incubation. Nature provides nesting birds with the instinct and we know turning is necessary in incubating machines to attain full hatching potential of the eggs.

Do you know why egg turning is necessary for good hatching?

The albumen (white) of an egg contains virtually no fat particles and has a specific gravity near that of water. The yolk, however, has a relatively high fat content. Fats and oils have specific gravities lower than water and float on water. The egg yolk tries to do the same thing -- float on the albumen. If an egg is left in one position, the yolk tends to float upward through the albumen toward the shell.

The developing embryo always rests on top of the yolk. When an egg is turned, the yolk turns in the albumen so the embryo is again positioned on top of the yolk. Nature probably does this so the embryo is always in the best position to receive body heat from the mother hen sitting on the eggs.

If the egg is not turned, the yolk tends to float upward toward the shell and pushes the embryo nearer the shell. If the yolk travels rises enough, the developing embryo is squeezed between the yolk and shell. The embryo can be damaged or killed. Turning the egg causes the yolk to be repositioned away from the shell, making it safe for the developing embryo until time to turn the egg again.

Strands of twisted albumen extend from the yolk into the albumen toward both the small and large ends of the egg. These strands are called chalazae. They help keep the yolk away from the shell. The chalazae hold the yolk firmly in the egg's center until egg quality begins to deteriorate, as when an egg is placed in a 100oF. temperature incubator.

As the albumen becomes more watery, the chalazae lose their ability to hold the yolk in place, making it more important to turn the egg often after incubation begins. In general, the need for turning begins when eggs are set and remains until two or three days before the eggs begin pipping.

In large commercial incubators the eggs are turned automatically each hour, 24 hours a day. Eggs in small incubators in the home sometimes get turned only twice a day, once in the morning and again in the evening. If manual turning, it is best to turn the eggs for an odd number of times each day (i.e., 3, 5 or 7 times). The longest period that the egg remains in one position is during the night hours. Turning an odd number of times will alternate the nights that the same side of the egg is uppermost.

Some producers open an incubator, pull out a flat tray, and run their hands over the eggs. This, to them, is turning the eggs. Actually it is only stirring the eggs, because there is no definite way to tell if the eggs are just rolled around or if they actually end up in a different position. Many of the eggs may not get turned at all -- just rolled around. Turning eggs in this manner can also crack the egg shells. Many chicks develop in eggs with cracked shells (only the shell, not the membranes) but not many will pip and completely hatch because dehydration occurs and makes the environment sticky. The chick doesn't have enough strength to pip and free itself from this sticky environment.

If using a relatively small incubator, you work away from home, and can turn the eggs only a few times a day, mark X on the top side of each egg with a pencil or felt tip pen. Each time you turn the eggs, visually check to see if each egg is actually turned by making sure the X ends up on the opposite side from where it was before turning. If using a machine that turns the eggs automatically, the eggs should be turned at least once every two hours. If the turning system is manual, turn as often as practical. Try to allow an equal time on each side.

Eggs should not be turned within three or four days of hatching. Chicks need to position themselves for pipping and do this better if allowed to remain still while that process takes place. The embryo is large enough by this time that it has used most of the yolk for food and is no longer in danger of being squeezed between the yolk and shell.


Egg Incubator, Chicken, and Poultry Resources