[Investigations on the excretion of antibiotics in goats' milk following therapeutic application].

OBJECTIVE

Data on the excretion of antibiotic residues following therapeutic drug dosages in lactating goats with clinical signs of bacterial infections are currently lacking. Therefore, this study aimed at monitoring the drug residue excretion of a subset of frequently used antibiotics in the milk of dairy goats following their therapeutic administration.

MATERIAL AND METHODS

Over a period of 4 months, milk samples (udder halves) were collected in 2 goat milk farms from animals treated with antibiotics in routine practice based on the diagnosis of a bacterial infection. The samples were examined up to 3 days following the withdrawal time point. The animals were classified in 3 groups depending on their clinical symptoms and treatment. Goats in group 1 (afebrile goats with various bacterial infections excluding the udder) were treated with intramuscular amoxicillin injection (n = 5). Animals in group 2 (mastitis catarrhalis) were treated with intramammary injection of oxacillin and ampicillin (n = 6). Group 3 consisted of a single goat diagnosed with mastitis. This individual was treated with cefquinome in accordance with the results of the antibiogram. Milk samples were examined qualitatively by using a receptor assay (Betastar) as well as a microbiological inhibitor assay (Brilliant black reduction test, BRT). The latter assay was also used to semiquanti-tatively analyse drug residue levels in samples from group 2.

RESULTS

Following intramuscular treatment with amoxicillin, drug residue levels were estimated to be very similar in both udder halfs. Elimination was complete 3 days after the end of the treatment period. Animals in group 2 showed significant differences between treated and untreated udder halves. However, the untreated halves still exhibited residue levels exceeding the maximum residue limits during the treatment period. In both group 2 and 3, all milk samples were tested negative for drug residues before the end of the withdrawal period.

CONCLUSION

In the present study, no evidence of prolonged residue excretion into milk of goats following therapeutic administration of antibiotics was detected. Both the receptor test and the BRT represent suitable methods for an efficient antibiotic drug residue testing in goat milk. Reliable testing was merely not attainable in cases of milk samples possessing highly altered organoleptic characteristics.