Like humans, cows must have babies in order to produce milk. In the dairy industry, they are kept in a state of almost constant pregnancy, and the calves that are born are taken from their mothers within hours. Females are usually kept to replace their mothers, and males are considered a byproduct. They are sold for veal or simply thrown away. (The veal industry was developed as a way to use these "extra" calves. Learn more here.) Two months after their calves are born, the cows are re-impregnated via artificial insemination and the cycle begins again.
Take time to remember those who never got to experience the joy of motherhood.