Effect of dietary daidzein supplementation on egg laying rate was associated with the change of hepatic VTG-II mRNA expression and higher antioxidant activities during the post-peak egg laying period of broiler breeders

Daidzein, a soy phytoestrogen, is a powerful antioxidant and has multiple biological activities. In this study, the improvement of egg laying rate by feeding daidzein was confirmed again in broiler breeder hens during post-peak egg laying stages, and the mechanism underlying this process was elucidated by the changes of relevant genes expression and the antioxidant status in liver. Three hundred 460-day-old broiler breeders were randomly assigned to 1 of 3 groups (100 birds/10 replicates/group) and were fed a basal diet (control, Con) or the basal diet supplemented with either 5 (low dosage, L) or 10 mg (high dosage, H) of daidzein per kg of diet. After one week adaptation to dietary daidzein, the experiment lasted for 15 days. Both low and high dosage of daidzein supplementation significantly increased the egg-laying rate (P<0.05), but did not change (P>0.05) body weight, oviduct weight, small follicles weight or the number of preovulatory follicles. Serum estrogen showed dose-dependent decrease by daidzein treatment and reached the statistical significance in H group (P<0.05). Serum triiodothyronine and thyroxine concentrations were not altered by daidzein (P>0.05). Daidzein reduced serum malondialdehyde content (P<0.05). In liver, total antioxidant capacity was greatly increased by daidzein (P<0.05), and the activity of glutathione-peroxidase was increased by high level of daidzein treatment (P<0.05), while the activity of superoxide dismutase and the content of malondialdehyde in liver were not changed by daidzein (P>0.05). Real-time PCR analysis showed that, in parallel with the increase of egg laying rate, down-regulation of vitellogenin-II and up-regulation of estrogen receptor ß mRNA expression in liver were observed in daidzein treated hens (P<0.05), while estrogen receptor a gene transcription was not affected (P>0.05). The results indicate that dietary daidzein supplementation improves egg-laying rate by increasing the antioxidant capacity and changing the relevant genes transcription in liver of broilers.