Oxytetracycline (abbreviated OTC) was fed to laying hens for 7 days at the dietary levels of 0, 20, 500, 1, 000, 2, 000 and 4, 000ppm, and OTC content in egg white and yolk laid on the 7th day was analyzed microbiologically. To the hens fed 4, 000ppm of OTC, OTC-free basal diet was fed for another 7 days and all of the eggs laid during 14 days of experimental period were analyzed for OTC content.
No OTC was detected in the eggs laid by the hens fed 20ppm of dietary OTC, which is allowed for growth promoting purpose.
Feeding the diets containing OTC at the level higher than 500ppm for 7 days, content of OTC in the eggs increased in proportion to the dietary OTC level. Average OTC content in whole eggs laid by the hens fed 4, 000ppm of OTC increased linearly after the start of OTC feeding, and decreased exponentially after the withdrawal of dietary OTC.
The similar equation was induced to describe the behaviour of OTC to the equation for spiramycin (SP). From the equation, it is suggested that about 10 times more dietary SP is transferred into eggs than dietary OTC, and that no OTC will be detected even on the 7th day, if dietary OTC level is less than 247ppm.
Biological half life of OTC in whole egg was 1.1 days with 95% confidence interval from 1.6 to 0.8 days, which is shorter than 2.4 days for SP, and similar to 1.3 days for tylosin.
Japan Poultry Science Association