Bang's disease (brucellosis) is caused by the Brucella abortus organism. It can markedly reduce fertility in cows and it can be contracted by humans as a disease known as undulant fever. Heifers should be vaccinated in calfhood to provide immunity from disease. Since most dairy cows are bred by artificial insemination there is little danger of a clean herd becoming contaminated from breeding. Persons drinking unpasteurized milk are taking a serious risk unless they know that the milk comes from a clean herd.