Intensive dairy production aims to produce high volumes of milk while keeping costs down. Cows are bred for high milk yeild. Dairy cattle are often culled and replaced after only three or four years, as the stress of constantly producing so much milk wears out their bodies very quickly.
Artificial insemination is used to promote high-yeilding genetics in the herd. Cow and calf are separated early to ensure that milk production is maximized for market. Calves are fed high-protein milk replacement instead. Female calves replace older dairy cows, and male calves are sent to veal farms.
Dairy cows undergo constant stresses owing to crowded, confined living conditions.
The Canadian Coalition for Farm Animals fact sheet on dairy cows provides more information.