P1638 Abstract (poster session) Concentrations and remediation of cephalosporin residues in waste milk from dairy farms in England and Wales R.A. Horton*, V. Bailey-Horne, M. Sharma, L. Randall, L. Brunton, J.R. Jones, K. Heinrich, M. Sharman (Addlestone, Sand Hutton, Carmarthen, UK)

Objectives: The objectives of this study were to determine the concentrations of cephalosporin residues in waste milk (milk unfit for human consumption, fed to calves) from dairy farms in England and Wales and to investigate potential methods for remediation by either heat treatment or adjustment of pH to decrease cefquinome residue concentrations prior to feeding to calves. Methods: Samples of waste milk were collected from 103 dairy farms in England and Wales, together with information on the antibiotics administered to the cows. Samples were stored frozen prior to quantitative analysis for cephalosporin residues by liquid chromatography–tandem mass spectrometry (LC-MS/MS). To investigate possible methods for remediation of waste milk which might be suitable for use on dairy farms to reduce residues, experiments were conducted on raw, unpasteurised milk that had been spiked with cefquinome sulphate (final cefquinome concentration 2 µg/ml). The effects of temperature and pH on the degradation of cefquinome were studied over a period of 10 days. Spiked milk samples were maintained at either 5, 18, 36 or 50°C for the temperature stability study, and adjusted to either pH 1, 4, 7, or 10 for the pH stability study. In each study aliquots of spiked milk were taken for analysis by LC-MS/MS after 0, 2, 4, 6, 8, 24, 48, 72, 120, and 240 hours. Samples were stored frozen at - 80°C prior to analysis. Results: Cefquinome (a 4th generation cephalosporin) was the most prevalent cephalosporin detected in waste milk, being detected in 21% of samples tested. Cefalonium, cefalexin and cefapirin (all first generation cephalosporins) were detected in 7.7%, 5.8%, and 2.9% of samples respectively. Overall, there was good agreement with the reported use of cephalosporins and the detection of cephalosporin residues (agreement for 95% of samples tested). Conclusion: This survey shows that cephalosporins are present in waste milk, a product often used for feeding calves on dairy farms in England and Wales and that cefquinome was the cephalosoporin most frequently detected. It has been suggested that cephalosporins in waste milk may select for cephalosporin-resistant bacteria in the intestine of calves that receive this milk. Practical measures to achieve enhanced degradation of cefquinome residues such as alteration of the milk storage temperature or pH adjustment are currently being investigated and will be presented at the meeting.