Effects of dietary Mn-methionine supplementation on the egg quality of laying hens

This study was conducted to investigate the effects of dietary manganese-methionine (Mn-Met) supplementation on the egg quality of laying hens. A total of 480 Jinghong-1 strain layers aged 53 wk were divided into 5 groups with 6 replicates of 16 layers. Birds in the control group were fed a diet supplemented with 60 mg Mn/kg in the form of MnSO4; the birds in other 4 experimental groups were fed a diet supplemented with 20, 40, 60, and 80 mg Mn/kg as Mn-Met, respectively. Dietary Mn-Met treatments significantly affected (P < 0.05) the albumen height, yolk color, and Haugh unit compared to those of the control diet. The Mn contents in the eggshell increased (P < 0.01) significantly by increasing the Mn-Met supplementation, whereas Mn content in eggshell was triple that in the yolk or albumen. Compared with the 60 mg/kg Mn-Met group, the transverse surface in the control group had (P < 0.01) a greater width of mammillary cones, and there were obvious cracks on the outer surface in the control. There was no difference (P > 0.05) in the eggshell gland (ESG) in the expression of calbindin-D-28k (CaBP-D-28k) mRNA in response to any diet treatment. In conclusion, dietary Mn-Met supplementation increased internal egg quality and the ultrastructure of the eggshell. Compared to the control, 60 mg/kg Mn-Met treatment resulted in improving egg quality, and 20 mg/kg Mn-Met treatment had similar effects the control treatment had on the egg quality. This indicates that the inorganic Mn can be replaced by the lower concentration of Mn-Met.