Because the peripartum and early lactation periods are times of high susceptibility of the mammary gland to mastitis, many immunization schedules include prepartum immunizations during the dry period when milk is not removed and the mammary gland undergoes involution. It is also important to remember that cattle are generally immunosuppressed during the peripartum period [88, 89] , potentially compromising the impact of immunizations administered just before or just after calving.