Restriction of cadmium transfer to eggs from laying hens exposed to cadmium

The transfer of Cd to eggs of white Leghorn laying hens has been shown to be restricted. After Cd was injected ip into laying hens, the Cd concentrations in the blood, livers, ovaries, and eggs were measured. Although the Cd concentrations in the maternal blood and livers increased remarkably at certain levels of administrations, the Cd concentration in the yolks of eggs was not significantly increased, and was less than 0.04 microgram/g wet weight. After egg production stopped in the highest injected group (7.5 mg Cd/kg), Cd in the yolks of eggs had an accumulated range of 0.02-0.03 microgram/g wet weight. This was despite the high Cd accumulation in the liver. Furthermore, the Cd concentration in the follicle walls of the ovary increased and was 13- to 52-fold higher than in the follicle yolks. An additional experiment was conducted in order to estimate whether hatching success is affected by the Cd in the laid eggs of Cd-injected laying hens. The ratio of hatching success in the 0.3 or 1.2 micrograms Cd/egg-injected groups was similar to that in the saline-injected group, indicating that a small amount of Cd in the eggs might exert no marked influence on the hatching success. In conclusion, Cd transfer from laying hen to eggs was restricted after the maternal bird was exposed to Cd. Furthermore, Cd accumulates in the follicle walls of ovary. These results suggest that the follicle walls might play a role in protecting the follicle yolks against Cd toxicity.