Poultry > Hatching & Embryology
Eggs are candled to determine the condition of the air cell, yolk, and white; to detect bloody whites, blood spots, or meat spots; or to observe germ development. Candling is done in a darkened room with the egg held before a light which penetrates the egg and makes it possible to observe the condition of the contents.
The candler should be set on a box or table at a convenient height (about 38 to 33 inches from the floor), so the light will not shine directly into the eyes of the operator. In candling, the egg is held in a slanting position with the large end against the hole in the candler. The egg is grasped by the small end and, while held between the thumb and tips of the first two fingers, is turned quickly to the right or left. This moves the contents of the egg and throws the yolk near the shell. Because of the color of their shells, brown eggs are much more difficult to candle than white eggs.
To do a reasonable job, an extensive knowledge of candling is unnecessary, particularly if the eggs are all relatively fresh. One should be able to distinguish a fresh egg from a stale egg, however, and to detect such abnormalities as bloody whites, blood spots, meat spots, and cracked shells. In a fresh egg, the air space is small, measuring no more than 1/8 inch in depth. The yolk shadow can hardly be seen and shows little motion. The white should be firm and clear. In a stale egg, the air space is larger and may have an irregular movable lower outline. The yolk shadow is plainly visible and moves freely. The white is thin.
Most newly laid eggs are of good quality. Eggs not over two or three days old, if held under good conditions, will meet the specifications for Grade A. This means that on most farms where eggs are given good care, about the only eggs to be removed by candling are those with bloody whites, blood or meat spots, and cracked shells.
In learning to candle eggs, the eye must be trained to look for the points enumerated and to note them quickly. With some practice, you can soon learn to recognize differences in interior egg quality.
Ken Koelkebeck Extension Specialist, Poultry
« Back to Poultry