Excretion of tetracycline and chlortetracycline in eggs after oral medication of laying hens

Abstract

After dosing laying hens orally with tetracycline (TC) through either drinking water (0.25 and 0.5 g/1 for 5 days) or feed (300 and 600 ppm for 7 days), and chlortetracycline (CTC) through feed (600 ppm) residues were determined by an agar plate diffusion technique in cylinders with Bacillus cereus as test‐organism, separately for albumen and for yolk. The sensitivity threshold was 0.07 μg/g in albumen and 0.15 μg/g in yolk for TC and 0.01 μg/g in albumen and 0.06 μg/g in yolk for CTC. Drug excretion via egg was 3‐fold higher for TC than for CTC. The drug was excreted preferentially into the yolk (about 75% of the total amount) and the elimination period lasted between 6 and 11 days for TC and 9 days for CTC, after treatment. Tetracycline use in laying hens is discussed, taking into consideration the proposals presented by the joint FAO/WHO Expert Committee on Food Additives.