Residue depletion profiles of selected penicillins in goat milk after therapeutic treatment

This study describes quantitative analyses of some penicillins in goat milk after therapeutic treatment of bacterial infections. Group 1 (systemic infections, n=5) had been treated intramuscularly with amoxicillin (AMX, 7 mg/kg b.w., 5x within 5 days), group 2 (mastitis; n=6) intramammarily with oxacillin/ampicillin (OXA/AMP, 40/20 mg, 4x within 4 days) in one udder half. Udder half milk samples were analyzed by enzyme immunoassays, with detection limits of 1 ng/ml (AMX), 30 ng/ml (OXA), and 2 ng/ml (sum OXA/AMP). AMX residues varied between 1 and 160 ng/ml during treatment, but fell below 1 ng/ml 1 day before the end of the withdrawal period. In all samples except one, AMX concentrations were below the European Union maximum residue limit (MRL, 4 ng/ml) as early as two days after the last application. OXA levels in treated udder halves varied widely during treatment (<30 ng/ml to 1.2 mg/ml). Milk from non-treated halves also contained OXA, but concentrations were lower (<30 – 410 ng/ml). OXA fell below the MRL (30 ng/ml) 1.5 days before the end of the withdrawal period. Combined analysis of OXA and AMP showed that total residues were well below 4 ng/ml at least 1 day before the end of the withdrawal period. This is the first quantitative report on OXA excretion in goat milk after therapeutic application under real life conditions of goat milk production. The milk of all analysed goats complied with MRL regulations after the withdrawal period of 4 days (OXA) and 4.5 days (AMX). • Antibiotic residue depletion in goat milk under real farming conditions • Therapeutic antibiotic treatment of bacterial infection in lactating goats • Quantitative residue analysis of penicillins by enzyme immunoassay • Residue levels below the MRL before end of the withdrawal period • No violative results in milk after extra-label use of amoxicillin