The Evolution of the Eggshell

10 hybrid ISA Brown hens, 50 weeks old, hold single in cages and fed with combined granulated forage, were monitored for a period of 3 weeks to establish the body weight, the egg laying time, the laying interval and the length of clutches for each hen. During this time the eggs were harvested and the eggs weight, eggshells weight, the calcium, phosphorus and magnesium eggshell content were determined. When 53 weeks old, the hens were divided into 4 groups depending on the time elapsed from the last oviposition for each hen and they were slaughtered. The eggs in different stages of development were sampled and the egg weight, the eggshell weight, the calcium, phosphorus and magnesium eggshell content were determined. Depending on the egg stage formation: at 10-12 hours postoviposition the eggshell mean weight was 2.15 g, i.e. 40.49%, the mean calcium content of the eggshells was 0.37 g calcium, representing 18.97% of the calcium content of the whole eggshell. At 22-23 hours after oviposition the eggshell weight was 6.13 g, representing 98.39% of the completely formed eggshell, the calcium content of the eggshells was 2.23 g (mean value), which represents 97.38% of the whole egg mineral shell.