COMPARISON OF THE EFFECTS OF THE DEGREE OF FOOD RESTRICTION DURING REARING ON OVARIAN-FUNCTION AT THE ONSET OF LAY IN UNSELECTED DUCKS (ANAS-PLATYRHYNCHOS) AND IN A LINE SELECTED FOR IMPROVED FOOD EFFICIENCY

1. Ovarian structure and function at sexual maturity in two lines of ducks (selected or not selected for juvenile food efficiency), fed ad libitum or restricted to achieve 0.50, 0.65 or 0.80 of unrestricted body weight at 24 weeks, were compared in a randomised block factorial experiment. 2. Selected ducks were larger but not fatter or older at sexual maturity, had, more yellow follicles, giving a greater potential for multiple ovulation, and a higher proportion of atretic yellow follicles, compared with unselected ducks. 3. There was a linear relationship between the number of normal yellow follicles and body weight at the onset of lay which was similar in the two lines. 4. Several birds on the most severe regimen failed to lay and it was concluded that ducks should be at least 0–6 of unrestricted body weight for the onset of lay. 5. Weight of the ovary with follicles less than 8 mm diameter was greater in selected compared with unselected ducks and in birds fed ad libitum compared with restricted ones. © 1990, Taylor & Francis Group, LLC. All rights reserved.