COMPLEX STUDY OF THE PHYSIOLOGICAL-ROLE OF CADMIUM .2. EFFECT OF CADMIUM LOAD ON THE CADMIUM CONTENT OF EGGS

The possibility of ''cadmium (Cd) contamination'' of eggs and the dyna mics of Cd accumulation were studied. A total of 40 (4x10) Japanese qu ails weighing 155-200 g, being at the middle phase of egg production a nd kept on batteries in a climatized animal house were used. The birds were fed a standard quail layer diet and drank tap-water ad libitum. With the exception of the control group (Cd-0), the diet of the other three groups was supplemented with Cd sulphate homogeneously mixed in the diet so that it contained 75 mg (Cd-75), 150 mg (Cd-150) and 300 m g (Cd-300) per kg. During the 37-day feeding trial the quails' behavio ur, health status and daily egg production were monitored and the bird s were weighed weekly. The egg production of the experimental groups, particularly of those exposed to a high Cd load, rapidly decreased: at the highest Cd load (300 ppm) egg production completely ceased at day s 10-11 of the trial. The total Cd content of the eggs rose already fr om the 3rd day of the feeding trial and by day 10 it reached a value o f 0.777 mg/kg dry matter in the eggs of quails of group Cd-75. This wa s about five times the value measured in the control quails' eggs (0.1 65 mg/kg dry matter). The Cd content of the egg-white and egg-yolk (ma ximum values: 0.212 and 0.107 mg/kg dry matter) also increased to abou t 2 or 3 times that measured in the control eggs. The Cd content of eg gs reached the peak in the 2nd week of the feeding trial, then started to decrease, and in the 3rd and 4th weeks not even the eggs laid by q uails exposed to a high Cd load contained more Cd than about twice the concentration measured in the controls' eggs. The elucidation of this hitherto not studied process requires further investigations. The phe nomenon may be due to a lack of the protein necessary for Cd transport and to the impairment of Cd absorption and of the excretory activity of the oviduct. The higher Cd concentrations measured in the egg were accompanied by markedly elevated Fe, K and S values. In the egg sample s collected in the 4th week a substantial reduction in Ca and P concen tration was observed. As regards the mineral elements measured in the egg-shell, a significant negative correlation was established between the concentration of Cd and those of Zn, Mg and Ca. Necropsy revealed severe emaciation, hepatic and renal degeneration. In many birds there was catarrhal enteritis, ovarian and oviductal atrophy. By light micr oscopic examination the follicular epithelial cells of the ovaries sho wed degeneration, atrophy of the glands in the tunica propria, tubulon ephrosis in the kidney, regressive changes of exocrine glandular epith elial cells of the pancreas, and osteoclastic osteolysis with degenera tion of osteoblasts in the tibiotarsal bone.