Age dependent differential effects of cyclophosphamide on natural antibody levels in chickens

Administration of 5 mg of cyclophosphamide per day for 4 days into neonatal chicks resulted in suppression of natural agglutinin titers up to at least 12 weeks of age. When the administration of cyclophosphamide was delayed until 7 days post-hatching suppression was found up to 8 weeks but titers rose to normal by 10 weeks after initial injections. Injections of cyclophosphamide after 21 days of age did not suppress natural agglutinin titers unless the drug was administered daily for 2 or more weeks.