“All poultry sourced for Pesach has to be fed on a non-wheat feed diet,” a spokesperson for the London Board of Schechita told the Jewish News. The board is a main purveyor of kosher meats and poultry in England.
The Orthodox Union kosher certifying agency in the United States also observes this restriction. Rabbi Zvi Nussbaum of the Orthodox Union said that all of their poultry are fed leavening-free food all year.
When wheat, barley, spelt, oat, or rye come in contact with liquid, they are considered chametz. Wheat-free poultry feed is used to prevent chametz from somehow making its way into the final product.