INFLUENCE OF PROLONGED TREATMENT PROTOCOLS ON MAXIMUM RESIDUE LEVELS OF AMOXICILLIN CONCENTRATIONS IN BOVINE MILK.

The aim of this study was to evaluate two off-label protocols for the treatment of bovine mastitis with regard to antibiotic residues in milk and length of withdrawal periods. Forty-eight udder quarters infected with Staphylococcus aureus, from 19 dairy cows were included in the study. The animals were divided into two groups (A and B); Group A received intramammary and systemic intramuscular treatment with amoxicillin while Group B received intra-mammary treatment only. The impact of the treatment regime on antibiotic concentrations in milk was evaluated. All cows received six intra-mammary injections with cattle-labelled injectors in 12-h intervals, whereas cows in Group A were additionally treated intra-muscularly twice in 24-h intervals. Milk samples were taken in 12-h intervals up to 120 hours after the beginning of treatment, which was considered to be a cut-off value for the withdrawal period. Amoxicillin concentrations were measured using a Waters Xevo Triple Quad mass spectrometer (QQQ) and a Waters UPLC. Amoxicillin concentrations were significantly higher in Group A than in Group B in all measured intervals. Antibiotic concentrations significantly decreased at 72 h (Group B) and 84 h (Group A) afterthe beginning of treatment. At theend of the producer-suggested withdrawal period, concentrations of amoxicillin were above MRL in 65% of udder quarters in Group B and in 40% of udder quarters in Group A. [ABSTRACT FROM AUTHOR]