A recent study in China investigated the effect of dietary manganese supplementation on eggshell quality. A total of 216 layers at the age of 50 weeks were divided into three groups.

In the first eight weeks of the 12-week feeding trial, all groups were fed a basal diet that met all nutrient requirements except for manganese. In the last four weeks of the trial, each group was fed one of three diets supplemented with manganese levels at 0, 25 or 100 mg/kg. Dietary manganese deficiency did not affect overall egg performance of layers. Dietary manganese supplementation significantly improved breaking strength, thickness and fracture-toughness of eggshells (P < 0.05).

In photographs of eggshell ultrastructure, the size of mammillary cones and cracks in the outer surface were decreased by dietary manganese supplementation. The measured indices of eggshell membrane quality were significantly increased by dietary manganese additions (P < 0.05), as was further confirmed by increased messenger RNA (mRNA) expression and protein expression of membrane proteins.

This study clearly indicated that dietary manganese supplementation improves eggshell quality by enhancing the quality and strength of the eggshell membrane, which affects the ultrastructure of eggshells.