Manganese supplementation enhances the synthesis of glycosaminoglycan in eggshell membrane: a strategy to improve eggshell quality in laying hens.

This study investigated the effect of dietary Mn supplementation on eggshell quality, ultrastructure, glycosaminoglycan (GAG), and uronic acid content, and mRNA and protein expression of Galβ1,3-glucuronosyltransferase (GlcAT-I). A total of 216 layers (Hy-Line Grey) at age of 50 wk were divided into 3 groups. In the first 8 wk of the 12-wk feeding trial, all groups were fed a basal diet that met all layer nutrient requirements except for Mn. In the last 4 wk, each group was fed 1 of 3 diets supplemented with Mn levels at 0, 25, or 100 mg Mn/kg. Dietary Mn deficiency did not affect the egg performance of layers. Dietary Mn supplementation significantly improved the 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 Mn supplementation. The contents of GAG and uronic acids in eggshell membrane were significantly increased by dietary Mn addition (P < 0.05). This result was further confirmed by increased mRNA expression and protein expression of GlcAT-I when Mn was added to the diet. This study suggests that dietary Mn supplementation can improve eggshell quality by enhancing the GAG and uronic acid synthesis in the eggshell glands, which can affect the ultrastructure of eggshells.