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Soya isoflavones are compounds with phytoestrogenic character - istics, i.e. because of their structure, their effects are similar to those of animal estrogens. This is why they are used for medicinal purposes in aging women. The presented experiment with laying hens was conducted to demonstrate the possibility of transferring soya isoflavones from feed into egg yolk to produce isoflavone-enriched eggs. Laying hens were randomly assigned to a control and 3 experimental groups and fed a basal diet or the basal diet supplemented with different concentrations of isoflavones: 1000, 2000 or 3000 mg · kg -1 feed. The transfer of isoflavones (daidzein and genistein) from the feed into the egg yolk of treated hens was found to be significant. At the end of the experiment, the content of the analysed isoflavones was from 396.0 to 412.4 μg.

Isoflavones are phytoestrogens which have estrogen-like activity in animals and humans. Because of this characteristic influence, the aim of this investigation was to examine the effect of genistein and daidzein on testicular weight and testosterone secretion in ISA Brown roosters. Genistein and daidzein as non-steroid phytoestrogens were added in large amounts to the feed of roosters. Soy isoflavones were added to rooster diets in amounts of 0, 300, 600, 1200 and 1800 mg/kg of feed. At the end of the 37th week no significant differences were found between the groups in testicular weight (P>0.05) and testosterone secretion (P>0.05) measured in the blood of birds. Blood testosterone concentration was significantly higher in younger (20-week-old) roosters than in 37-weekold roosters (P