At the age of 24 weeks, 60 Pekin type ducks, line P66, were divided into 6 flocks (1 drake and 9 ducks). A control and an experimental group were formed, each comprising 3 flocks. Both groups were fed a standard diet, but that of the experimental group was supplemented with 500 mg vitamin C/kg. Ducks from the experimental group exhibited a significantly higher erythrocyte count (on average, by 0.16×10¹²/L) in blood collected in weeks 5, 11 and 17 of the experiment. The haemoglobin level in the blood of birds from this group measured in week 17 was 0.73 mmol/L higher than in the control group. Both egg fertilization as well as duckling hatching from fertilized eggs obtained from ducks in the experimental group (on the third hatch) were higher, while the number of crippled ducklings was smaller. The erythrocyte count in the blood of one-day-old ducklings derived from the ducks fed vitamin C-supplemented diets was significantly higher, on average, by 0.14×10¹²/L. In addition, in comparison with the control group, the haemoglobin level in the blood of ducklings derived from ducks in the experimental group and hatched from eggs set in weeks 4 and 11 of the experiment was 0.74 and 1.04 mmol/L higher, respectively. The ducklings derived from the experimental group of ducks and hatched from eggs set in week 18 of the experiment had a 2.5 percentage point higher haematocrit value.