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In the combat against bacterial resistance, there is a clear need to check the use of antibiotics in animal husbandry, including poultry breeding. The use of chicken feathers as a tool for the detection of use of antibiotics was investigated. An extraction method for the analysis of oxytetracycline (OTC) from feathers was developed and was tested by using incurred feathers obtained from a controlled animal treatment study. The use of McIlvain-ethylenediaminetetraacetic acid buffer only in combination with acetone gave the highest extraction yield, indicating the need of an organic solvent for feather extraction. By using the developed method, it was found that after a withdrawal time, the OTC concentration in feathers is in the mg kg⁻¹ range, far higher than that in muscle and liver tissue. Based on the analysis of individual segments of feathers from OTC-treated chicken, evidence was found supporting the hypothesis of secretion of antibiotics through the uropygial gland and external spread over feathers by grooming behaviour. It was also found that part of the administered OTC is built into the feather rachis. Finally, we provide the first evidence that the analysis of individual segments of the rachis can be used as a tool to discriminate among different treatment strategies, for example, therapeutic versus subtherapeutic. As a result, we concluded that the analysis of feathers is an extremely valuable tool in residue analysis of antibiotics.

len. Validation and application of a robust yeast estrogen bioassay for the screening of estrogenic activity in animal feed. Food Additives and Contaminants, 2006, 23 (06) . All of these blank and low estrogen spiked feed samples fulfilled the CCα and CCβ criterions, meaning that all 20 blank feed samples gave a signal below the determined decision limit CCα and were thus classified as compliant and at least 19 out of the 20 spiked samples gave a signal above this CCα (β=5%) and were thus classified as suspect. The method was specific and estrogens in feed were stable for up to 98 days. In this study we also present long-term performance data and several examples of estrogens found in the routine screening of animal feed.

A number of metabolites of 17b-estradiol were tested for their estrogenic activity using the ER-CA-LUX assay based on the increased expression of luciferase in exposed T47D breast cancer cells. E 2 b and estrone showed similar potencies in the test, whereas E 2 a was 100 times less active. Incubation of cells with estrone (0.35 mM) resulted in the formation of E 2 b, whereas the reverse reaction was observed for E 2 b. The resulting equilibrium may explain the similar estrogenic potency of estrone in the test. The synthetic 17-hydroxy benzoate ester of E 2 b was 3 times less active than the parent compound. The 17-hydroxy palmitate and oleate esters of E 2 b, were respectively 25 and 200 times less active than the parent compound. The 2-hydroxy metabolites of E 2 b and estrone showed a 5,000 to 10,000 fold lower activity. The 4-hydroxy metabolites were more potent than the 2-hydroxy metabolites, showing only a 20-200 times lower activity. The 2-and 4-methoxyesters of estrone were 700 times less active. It is concluded that the estrogenic potency of metabolites formed in cattle after treatment with E 2 b, like estrone, E 2 a and especially the esters of E 2 b, may be significant with respect to the potential risk of the use of estradiol for growth promotion in domestic animals in certain countries.Key words: Estrogenicity; ER-CALUX; catecholestrogens; estradiol; estradiol-esters. L. A. P. Hoogenboom, RIKILT, Bornsesteeg 45, 6708PD Wageningen, The Netherlands, e-mail: L.A.P. Hoogenboom/rikilt.wag-ur.nl The use of 17b-estradiol for growth-promoting purposes in cattle may result in the increased formation of residues of not only the parent compound but also its metabolites. In order to investigate the potential risk for the consumer, it is essential to obtain information on the identity, levels and biological properties of these compounds. In cattle the major metabolites of E 2 b are estrone, the 17a-congener and their glucuronide conjugates (1-3). Previous studies showed increased levels of the parent compound, and the two major bovine metabolites,