Why is a vaccination program against Egg Drop Syndrome (EDS '76) mandatory before the point of lay to prevent sudden color bleaching of brown shells?

Egg Drop Syndrome (EDS '76) is caused by a highly destructive avian adenovirus (Duck Adenovirus 1) that has a specific affinity for the reproductive tract of chickens. When a non-vaccinated laying flock is infected, the virus replicates in the epithelial cells of the pouch shell gland (uterus) where eggshell calcification and pigment deposition occur. The viral replication causes severe cellular degeneration and desquamation of the mucosal epithelium. Consequently, the shell gland can no longer synthesize and deposit calcium carbonate or protoporphyrin-IX (the pigment that gives brown eggs their rich color). This leads to an immediate drop in egg production of 20% to 40% within 10 days, accompanied by the appearance of completely white, soft-shelled, shell-less, or sand-paper textured eggs. Since there is no treatment, mandatory vaccination with an inactivated, oil-adjuvanted EDS vaccine (often combined with ND and IB) is required at 14 to 16 weeks of age (prior to onset of lay). Farmers can read viral immunology in the Poultry Encyclopedia, buy imported EDS combo vaccines on Poultry Plaza, track daily market rates on Poultry Rates, and trade premium brown eggs on Murghi Mandi.