Effect of daidzein on egg-laying performance in Shaoxing duck breeders during different stages of the egg production cycle

1. The effect of a phyto- oestrogen, daidzein, on the laying performance of Shaoxing female ducks was examined in three experiments performed at different stages of the egg production cycle. Egg- laying rate, egg weight, egg composition, feed conversion ratio, hatchability characteristics of eggs and body weight, ovary and oviduct weight, as well as changes in serum concentrations of T-3, T-4 and E-2 were recorded as response criteria. 2. In the first experiment, 68 young ducks, 100 d of age, were given a basal diet ( maize - soybean meal) with or without 3mg of daidzein/ kg diet for 42 d. Daidzein did not affect the onset of lay but apparently decreased egg- laying rate and mean egg weight as well as the feed conversion ratio. 3. In the second experiment, 240 breeding ducks, 402 d of age, were allotted at random to three groups and given the basal diet containing daidzein at 0 ( control), 3 ( Da1) and 5 mg/ kg ( Da2) for 35 d. Egg- laying rate, mean egg weight and feed conversion ratio increased in both Da1 and Da2 groups. However, an adverse effect of daidzein on fertility and hatchability was observed. 4. In the third experiment, 320 breeding ducks, 415 d of age, were fed on the basal diet with or without 5 mg of daidzein/ kg diet for 63 d. Egg- laying rate increased by 7.7%, average egg weight tended to increase, whereas yolk/ albumen ratio decreased. Daidzein- treated ducks had higher body weight and oviduct weight compared with their controls. Elevated plasma T-4 and E-2 concentrations accompanied these phenotypic changes, but serum T-3 was not affected. 5. It is suggested that daidzein exerts divergent effects on the egg- laying performance of Shaoxing ducks under different physiological conditions and this action is dose- dependent. The changes in circulating E-2 imply possible participation of endogenous oestrogen in the mechanism of daidzein action.