Productive life and reasons for disposal of Holstein cows selected for large versus small body size.

Holstein cows were compared for direct and correlated responses to selection for large versus small body size. The divergent selection lines differed for body weight, body dimensions, and birth weight of calves but did not differ for production or calving ease. Also, cows in the small line required fewer services to conception during first lactation than did cows in the large line. Cows in the body size lines differed for three reasons for disposal: udder conformation, which favored cows in the large line; problems with legs and feet, which favored cows in the small line; and a miscellaneous category, which included internal infections and favored cows in the small line. Productive life to a maximum of 6 yr was 87.7 d (15.4%) longer for cows in the small line than for cows in the large line. Continued selection for larger Holstein cows in North America might not be economically justifiable.