Brucellosis is a contagious, infectious, and communicable disease that primarily affects cattle, bison, and swine, and is caused by bacteria of the genus Brucella. In cattle, water buffalo, and bison, it is caused almost exclusively by Brucella abortus. The disease causes loss of young through spontaneous abortion or birth of weak offspring, reduced milk production, and infertility. It can be transmitted from animals by direct contact with infected blood, placentas, fetuses, or uterine secretions, or through the consumption of infected and raw animal products (especially milk and milk products) . There is no economically feasible treatment for brucellosis in livestock.

Young cattle within a herd often abort within a relatively short timeframe, referred to as an "abortion storm". The disease is also known as “contagious abortion” . People infected with the bacteria that causes bovine brucellosis can develop fatigue, headaches, high fever, chills, joint pain, backache, and orchitis (in males) . These symptoms may persist for several weeks to months or years if not treated. Brucellosis is one of the most widespread zoonoses transmitted by animals and in endemic areas, human brucellosis has serious public health consequences. In the general population, most cases are caused by the consumption of raw milk or its derivatives such as fresh cheese.

Prevention and control of brucellosis in cattle involves regular serologic testing and elimination of reactors ("test and slaughter" programs) . Vaccination of young animals is ceased near the end stages of eradication campaigns to reduce the frequency of false-positive serologic test reactions. In California, female dairy breed cattle living within or entering the state must be vaccinated by the age of 12 months. Unvaccinated dairy breed heifers over 12 months of age may only be sold for slaughter; either directly, or to an approved feedlot for feeding to slaughter.