In the study, three separate herds were established: one of animals with a high rate of growth in their first year, one with animals that had shown low growth, and one randomly selected as a control group. These were called the High Line, the Low Line and the Control Line respectively. The Low Line herd started with 85 cows and some young bulls, and was closed to additions of other stock from 1974; it eventually numbered more than 400. To exclude possible effects of climate from the study, some stock was reared at Glen Innes in northern New South Wales and at Hamilton, Victoria. The experiment ran for nineteen years, by the end of which the Low Line animals were on average some 30% smaller than the High Line group.