Oxytetracycline residue levels in chicken eggs after oral administration of medicated drinking water to laying chickens.

Twenty laying birds were divided into four groups (n = 5) and given drinking water containing 0, 400, 600, and 800 mg/l of oxytetracycline respectively for 7 days. Eggs were collected continuously for 17 days after drug administration and stored at +4 degrees C. The oxytetracycline residues in yolk and albumen were analysed using a microbiological method with Bacillus cereus var. mycoides ATCC 11778 as the test organism. The mean maximum concentration of oxytetracycline was observed 2 days earlier in the albumen than in the yolk. The mean values in yolk and albumen were 0.526 and 0.280 mg/kg respectively. The depletion period was shorter for albumen than for yolk and oxytetracycline was detected in the yolk and albumen up to days 13 and 10 respectively. Withdrawal periods depended on the concentration of the antibiotic administered. Oxytetracycline residues reached a peak faster in albumen than in yolk, although the residues persisted for longer periods in the yolk.