Nowadays more and more people choose the industry of raising chickens, and feed is the main factor determining the quality of eggshells and the strength of eggshells. Most people generally believe that the calcium content of the laying hens is 3.2% to 3.5%, and the phosphorus content is 0.45%, which is the best level. In the hot season or the peak of egg production, the calcium content can be increased to 3.6%-3.8. %, adding 4% in a short period can make the eggshell thicker, but further increase is not good for laying eggs, and it can not improve the quality of eggshells.

Insufficient calcium in the feed promotes feeding, resulting in excessive feed consumption, more fat deposition in the hen, and increased body weight; excessive calcium in the feed can reduce the appetite of the chicken. In general, calcium ingested by chickens in the morning passes through the digestive tract and is absorbed into the bloodstream in the small intestine, deposited in the bones, and used to form eggshells when necessary. Calcium in the afternoon can directly form the eggshell. It is therefore best to feed the hen every afternoon or evening.

Shell and stone powder are used as calcium sources in production. Eggshell strength is best when the dietary calcium source accounts for two-thirds of the shell and limestone accounts for one-third. Chickens have the best absorption of animal calcium sources and the worst absorption of plant calcium sources. High temperature sterilized eggshells are the best source of calcium. The lack of vitamin D3 destroys the homeostasis of calcium and forms eggs with defective eggshells, so a sufficient amount of vitamin D3 is added to the feed in poultry cages for sale.