Most people have small herds. I often see people tending only one or two cows. Since that is their whole day's work, that cow's production is valuable. A Serb woman tends her milk cows in Pones. Some Kosovars have only one or two cows and depend heavily on the animals for their livelihoods.
Few farmers can afford to keep their own bulls for breeding.
So neighbors often share a bull or rent the services of one. If that bull becomes infected with brucellosis, it can spread the disease to every cow it encounters. In Montana, where we live, ranchers run huge herds of cattle. To avoid the spread of brucellosis most ranchers use only fresh bulls for breeding, ones that have never been used with other herds. Cows that are not ear-tagged and tattooed by a veterinarian as proof of having the brucellosis vaccine when they were calves cannot be sold out of state for breeding.