Disease results when management and environmental conditions favor their transmission and reduced resistance in the calf. In fact many of these organisms are present on many, if not most, farms but may not cause enough loss to be recognized until conditions are favorable for an outbreak of scours. Calf scours were not identified as a significant problem except on one farm on which Salmonella in scouring calves was also identified. Immunity to most infections is seldom absolute. Vaccines may prevent disease but not prevent infection.
Vaccines are tools used to raise the resistance of an animal to an infectious agent.
Presently, vaccines for some of the infectious agents that cause calf scours are available. They may be given to the cow before calving, or to the calf, depending upon the product. It is important to remember that an immune response takes time to occur. Most vaccines require two initial doses about 4-6 weeks apart and annual boosters for best results. Unfortunately, the disease agents that cause serious calf scours usually attack in the first week or two of life - too quickly for most vaccines to stimulate protection if given to the calf.