Caesium and iodine metabolism in lactating cows under chronic administration

1) Two Jersey cows were fed during 90 days with contaminated hay harvested in the South-East of France and containing about 5500 Bq/kg of dry matter (134 Cs + 137 Cs). A plateau was observed in milk 15 days and in meat 50-60 days after the beginning of the contamination. The transfer coefficients were at that time 1.1% for the milk and 2-2.7% for the meat. A calf was fed from the 8th day after birth until the 80th day solely with the contaminated milk from the two cows. At that time and weighing 130 kg it retained more than 40% of the ingested caesium. From the 44th till the 80th day the daily intake of milk was constant: in these conditions the transfer coefficient to meat was 16%. 2) Transfer coefficients to milk and thyroid were determinated in three Friesian cows contaminated daily with Na131I in pellets, one month before and two months after calving; one more lactating cow was contaminated for one month, 5 months after calving. The parturition provokes a fall of about 40% in the thyroid burden of the cows followed by a return near the initial equilibrium level (2-3 times the daily uptake in summer and 1 time in winter). At birth the ratio between the specific radioactivity of the calf thyroid and the cow thyroid was about 3. Transfer coefficients in milk at the equilibrium (one month after calving) were 0.35-0.50% in summer and 0.75-1.25 in winter.