Bovine respiratory disease (BRD) has a multifactorial etiology and develops as a result of complex interactions between environmental factors, host factors, and pathogens. Most outbreaks of pneumonia probably occur because calves have been exposed to large numbers of microbes, against which they have no protective antibodies, under adverse environmental conditions that have lowered the calves‘ resistance to disease. The intranasal administration of vaccine stimulates a strong immune response because vaccine antigens are delivered directly to mucosal surfaces in the nose – the major sites of immune response in cattle.