Transfer of Dietary Spiramycin into the Eggs and its Residue in the Liver of Laying Hen

Spiramycin was fed to layers at various dietary levels from 20 to 1, 000ppm for 7 days, and then dietary spiramycin was withdrawn and basal diet was fed for another 7 or 12 days. Spiramycin content in white and yolk of eggs laid by individual hen during and after the feeding period of spiramycin was analyzed microbiologically. Five hens each day fed 1, 000ppm of spiramycin were sacrificed at 0, 2, 4, 6 and 12 days after the withdrawal of dietary antibiotic for microbioassy of spiramycin content in the liver.The amount of spiramycin transferred into egg increased linearly with days on the antibiotic and increased also in proportion to dietary level of spiramycin. After the termination of antibiotic feeding, spiramycin in the egg decreased exponentially. Spiramycin content in liver decreased also exponentially after the withdrawal of dietary spiramycin. From these findings, an equation is introduced, by which spiramycin level in an egg laid on a certain day can be predicted. Biological half life of spiramycin in chicks body is estimated to be 2.4 days from the egg, which is agreeable to that estimated from the liver.