Effect of age on eggshell color and Haugh unit of eggs, protoporphyrin IX and ovomucin deposition and related gene expression in Hyline Brown laying hens.

Abstract

Objective: This study was conducted to investigate the effects of age on eggshell color, Haugh unit, and underlying mechanism in Hyline Brown laying hens.

Methods: A total of 192 Hyline Brown laying hens at 165 (D165 group), 307 (D307 group), or 475 (D475 group) days of age were divided into 3 groups with 8 replicates of 8 birds each, and fed the same diet for three weeks.

Results: Compared to the D165 group, the D307 and D475 groups had higher (p<0.05) eggshell L* value and yolk ratio but lower (p<0.05) albumin ratio; the D475 group had higher (p<0.05) eggshell b* value but lower (p<0.05) albumin height, Haugh unit and eggshell a* value. The D165 group had higher (p<0.05) eggshell protoporphyrin IX content and ovomucin content in eggs than the D307 and D475 groups. The D165 group showed higher (p<0.05) total superoxide dismutase activity and glutathione content in eggshell gland compared to the D307 group. The malondialdehyde contents in serum, eggshell gland and magnum were higher in the D475 group than in the D165 group (p<0.05). The D307 and D475 groups had lower (p<0.05) mRNA levels of genes related to pigment synthesis and transport (coproporphyrinogen oxidase, aminolevulinic acid synthase-1 and ATP-binding cassette subfamily G member 2) than the D165 group. The D475 group had lower (p<0.05) mRNA levels of genes related to albumin synthesis (α-ovomucin and lysozyme) than the D165 and D307 groups.

Conclusion: As hens aged, the deterioration of eggshell color and Haugh unit of eggs resulted from decreased gene expression and secretion of protoporphyrin IX and ovomucin, which could be attributed to increased lipid peroxidation in eggshell gland and magnum.