Assessment of Serum Neutralizing Antibody Titers against Foot-and-Mouth Disease Virus A and O in Young Colostrum-Fed Dairy Calves

oot-and-mouth disease (FMD) is an acute and highly contagious viral disease caused by a picornavirus that infects cloven-hoofed animals (1). The causative agent of this disease belongs to the Aphtovirus genus in Picornaviridae family (2). Clinical signs of FMD are fever, anorexia and vesiculation, mostly in the mouth, feet and teats (3). Although the mortality rate of this disease is low (except in young animals), FMD is a major worldwide animal health problem because of the highly communicable nature of the disease, and severe losses in the production of animals. Therefore, FMD is a perpetual menace to animal health of FMD-free-countries and disease management programs are very important, whereas regular large-scale vaccination is the current strategy for endemic areas, such as Middle East countries, Africa and South America. Maternal passive antibodies transmit to a calf by its dam during colostrum feeding (4). These colostorally derived antibodies that present in the beginning stage of animal life, block replication of FMD virus and protect against infection during the first months of life. Ipso facto clostoral antibodies are also important factor related to primary vaccine failure. The rate of passively acquired clostoral antibodies has a critical role in duration of passive protection. As clostoral antibody titers wane, susceptibility of the infection increase (5, 6). Therefore determination of the earliest age at which high rates of immune responses can be obtained, is very important. Some studies indicated range of level of clostoral antibodies and proposed strategies of FMD vaccination. To date, however, there are no studies in this field on Iranian foot-and-mouth disease virus (FMDV) vaccines. The aim of this study was to identify the best age of vaccination with Iranian FMDV vaccine containing aluminum hydroxide adjuvant, by identifying the serumantibody titer of young animals and their dams. The vaccine was produced by Razi Vaccine and Serum Research Institute (Tehran, Iran). The vaccine was supplied as bivalent containing Opan asia and A87 strains and aluminum hydroxide adjuvant. FMD viruses, strains Opan asia and A87 were grown in heteroploid hamster kidney (BHK-21) cells. The viruses were assayed by TCID50 method and used in virus neutralization (VN) test. The study conducted on three dairy cattle farms (farms 1, 2 and 3) situated in the karaj area in Iran. Two experiments (A and B) were performed to compare serum neutralizingantibody titer of young animals and dams. Blood samples were taken from the newborn calves and their dams immediately after birth. Calves were allowed to suckle their dams, and were bled from the jugular vein every month F