What are the principles for body weight control in broiler breeders?

In the first 6 weeks, body weight should be kept near the middle limit of the standard body weight range; from 7 to 15 weeks of age, it should be kept at the lower limit of the standard body weight, with body weight gain from 7 to 12 weeks of age falling within the lower limit of the restricted-feeding body weight range, and from 12 to 15 weeks of age body weight rising along the lower limit of the standard body weight, at which time feed restriction is most strict; from 16 weeks of age to two weeks before the start of laying, it should be kept at the upper limit of the standard body weight range.