Relationship between eggshell thickness and other eggshell measurements in eggs from litter and cages

The objective of the present study was to determine the relationship between eggshell thickness and other eggshell characteristics in eggs produced in litter housing system and enriched cages. Eggs were collected from 200 birds of ISA Brown genotype at 40-42 weeks of age. Half of the birds were housed in enriched cages (750 cm(2)/hen, 10 hens/cage) and the other half were housed in littered pens (9 hens/m(2), 10 hens/pen). Eggs in each housing system were split into three categories varying in shell thickness: the first category (thin shells 0.28-0.30 mm), the second category (medium shells 0.33-0.36 mm) and the third category (thick shells 0.39-0.41 mm). Results indicated that eggshell parameters differ significantly according to eggshell thickness. Significant interaction of shell category and housing system were observed in eggshell strength. As expected, the eggshell strength was increased with eggshells becoming thicker. Moreover, eggs with the thickest shells from enriched cages had significantly stronger shells than those from litter system. Eggshell weight was significantly increased in the thick eggshell category being higher in enriched cages (7.23 g) than in litter system (5.14 g). The Pearson's correlation coefficients showed a positive correlation between eggshell parameters and eggshell thickness in both housing systems. Moreover, the correlation between eggshell thickness and eggshell strength was higher on litter (0.64, p < 0.001) in comparison with enriched cages (0.48, p < 0.001). Results of the present study indicated that in thin shells, housing system plays an important role in determining the eggshell strength.