Modeling residue uptake by eggs .1. Similar drug residue patterns in developing yolks following injection with ampicillin or oxytetracycline

This study was conducted to model the pattern of antibiotic drug uptake within yolks of developing follicles. In two separate experiments, 16 hens were divided into equal groups (n = 8) and injected only once with either 400 mg/kg ampicillin or 200 mg/kg oxytetracycline (OTC: total hens = 32) approximately 1 h after oviposition. Twenty-four hours following injections, hens were euthanatized and the ovaries were collected. Yolks were dissected free from the individual follicles with a blunt probe. Individual large yellow yolks (greater than or equal to 0.2 g) and a pool of 5 small yellow yolks (< 0.2 g) were collected for determination of ampicillin or OTC content. Samples were prepared and assayed using an agar diffusion microbiological method. Selected parameters were not different (P > 0.05) between Experiments 1 and 2 and the data were combined. Results indicate that short-term drug exposure in hens produced incorporation of drug residues in developing yolks in a specific pattern that does not appear to be drug dependent (P > 0.05). These incurred residues are contained in developing yolks that are days to weeks from being ovulated. Drug residues were greater (total microgram content) in some of the less mature yolks vs the largest preovulatory yolk. This may lead to a sequential release of eggs with increasing residue content, even after drug withdrawal. These data were used to construct a model to predict the pattern of incurred residues in formed eggs following a hen's exposure to drugs or other contaminants.