The life of a dairy farmer is usually a rigorous one. Cows must be milked and other chores done seven days a week throughout the year. Hand milking has given way to the use of milking machines, but it must still be done twice a day. Family labor frequently makes up a large part of the labor force, especially on an average-sized farm. The sons and daughters of dairy farmers sometimes learn to put in long days and to carry heavy responsibilities at a young age. Since the middle of the 20th century, there has been a great decrease in the number of dairy farms in the United States and Canada. In general, however, the farms remaining are large, have highly productive cows, and are managed with great skill. These farms represent the survivors in a very competitive business.