Since the specific gravity of the shell is more than two times higher than the other parts of the egg, the percentage of egg that is shell has a major influence on the specific gravity of the whole egg. As the amount of shell increases, the specific gravity of the egg increases, and corresponding changes in the proportions of yolk, albumen, and shell membranes will be of little consequence. Egg specific gravity, therefore, is a good indicator of percentage shell and is the reason specific gravity is used to determine shell quality. At times a breeder manager or hatchery manager may wish to assess the status of egg shell quality for a particular flock or flocks. To perform the specific gravity determination, you immerse the egg in a series of increasingly concentrated salt solutions until the egg floats on the surface of one of the solutions.
Specific gravity is highly related to the incidence of breaks and cracks.
The incidence of breakage is above normal if the specific gravity of a flock averages less than 1.080. It should be adequate that we use two to three salt solutions to give us an estimation of the specific gravity of a flock's eggs. The day before the measurements are performed a minimum of 100 fresh eggs should be randomly selected from the flock. Avoid selecting only the better or poorer eggs from the flock. The eggs selected and the water to make the solutions should be placed in the room where the measurements will be performed the day before the test.