Most “ridged,” “sunburst,” “slab-sided,” soft-shelled, or double-shelled eggs are the result of eggs colliding in the shell gland region of the oviduct when an ovum (yolk) is released too soon after the previous one. Necropsy examinations have demonstrated that two full-sized eggs can be found in the shell gland pouch. As the second egg comes in contact with the first, pressure is exerted, disrupting the pattern of mineralization. The first egg acquires a white band and chalky appearance, while the second egg is flattened on its contiguous surface (ie, slab-sided). Pimpled or rough eggs may have been retained too long in the shell gland. Blood spots result when a follicle vessel along the stigma ruptures as the ovum is being released. Meat spots occur when a piece of follicle membrane or residual albumen from the previous day is incorporated into the developing egg.
Many abnormalities appear to have no specific cause, but the incidence is much higher in hens subjected to stressful management conditions or rough handling (catching or vaccination) during production. A significant increase in the number of soft-shelled eggs is also common as a result of viral diseases such as infectious bronchitis, egg drop syndrome, Newcastle disease, avian pneumovirus, and avian influenza.
Occasionally, small eggs with no yolk form around a nidus of material (residual albumen) in the magnum of the oviduct. Small eggs with reduced albumen and eggs with defective shells may be the result of damage to the epithelium of the magnum or shell gland.
Very rarely, foreign material that enters the oviduct through the vagina (eg, a roundworm) may be incorporated into an egg.