Six males and 24 female Cherry Valley Pekin ducklings were randomly allocated to each of 12 pens to test the effects of quantitative food restriction during the rearing period on the subsequent reproductive performance. At the end of the laying period (60 weeks) a "forced moult" was introduced and its effect on a further 40 weeks production investigated. 2. The 3 rearing treatments were 50% of ad libitum intake from 3 to 20 weeks; 75% of ad libitum intake from 3 to 20 weeks and ad libitum intake throughout. During the laying period (20-60 weeks) and post forced-moult period (60-100 weeks) duck breeder pellets were fed ad libitum to all groups. 3. Highly significant (P < or = 0.01) differences in favour of the restricted groups over the ad libitum-fed groups were observed in most of the responses studied. The following were the main advantages of food restriction: lower lifetime food intake, lower carcase fat content at 20 weeks, delay in sexual maturity, higher egg production, higher peak and terminal production, higher fertility, higher hatchability of eggs set and lower mortality. Egg mass and hatchability of fertile eggs was not influenced by food restriction in this experiment. The use of a "forced moult" showed that it could be of economical importance. 4. Difference between treatments in respect of absolute and relative visceral masses were also investigated. The absolute masses of the intestine, heart, gizzard and liver all decreased as the degree of food restriction increased. The relative visceral masses showed the opposite trend with the exception of the heart which showed no significant differences between treatments.
