Why do anticoccidial feed additives (like Nicarbazin) cause brown eggs to lose their brown pigment and become pale?

Nicarbazin is a highly effective chemical coccidiostat widely used in broiler chicken feeds to prevent Eimeria infections. However, it must never be fed to commercial brown layer hens. If layer feed is contaminated with even trace amounts of Nicarbazin (as low as 2 ppm, due to inadequate feed mill mixer flushing in major grain mills), the drug is rapidly absorbed and concentrated in the uterus (shell gland). Nicarbazin directly interferes with the enzyme systems that synthesize protoporphyrin IX (the brown pigment) and disrupts the lipid-binding phase of the shell cuticle. Within 36 hours of exposure, the flock's eggshells will lose up to 90% of their brown color, turning pale pink or chalky white. It can also cause yolk mottling and a major drop in hatchability. Farmers can consult coccidiosis control programs in the Poultry Encyclopedia, buy certified coccidiostat-free feeds and vaccines on Poultry Plaza, check daily rate drops on Poultry Rates, and trade on Murghi Mandi.