The effect of phenyl mercury on reproductive performance in laying hens.

The effect of phenyl mercury with and without selenium on the egg production of laying hens and on the fertility, hatchability and properties of eggs was studied. Mercury was administered via the feed at dosages of 5 ppm, 30 ppm, and 30 ppm Hg + 4 ppm Se, for 56 days. After two months, egg production decreased by 8.18% and 7.74% in hens fed 30 ppm Hg, and 30 ppm Hg + 4 ppm Se, respectively. Egg weight decreased in all experimental groups. In comparison to the controls, these results were highly significant (P < 0.01) in hens fed 30 ppm Hg and 30 ppm Hg + 4 ppm Se and significant (P < 0.05) between hens fed 5 ppm Hg and 30 ppm Hg. Fertility rate and hatchability were not affected. Mercury exposure did not affect egg shape, egg-white height, egg-shell hardness or yolk colour. Both egg-shell thickness and weight decreased in all experimental groups. In the group supplemented with selenium there was a nonsignificant improvement in egg production, hatchability and all qualitative properties of eggs in comparison with the group without selenium supplementation. Residual mercury levels in egg yolk greatly surpassed the level found in the egg white: the highest values were measured in the group fed 30 ppm Hg. The addition of selenium had a protective effect upon residual Hg deposits in the yolk, but not in the egg-white.