Antibiotic residues in milk and cheeses after the off-label use of macrolides in dairy goats

The limited availability of drugs registered for dairy goats makes veterinarians prescribe off-label treatments with a legally established minimum safety period of seven days. The aim of this work was to verify if the exceptional use of macrolide antibiotics in dairy goats generates residues in milk and cheeses within that period. Hence, three macrolide drugs (erythromycin, tylosin and spiramycin) were administred in an in vivo experiment in dairy goats. Ripened cheeses were made from bulk milk obtained before drug administration, 24 h after treatment, and at the end of the recommended withdrawal period. Residual amounts of erythromycin (234.9 ± 52.7 μg/kg), tylosin (198.7 ± 57.8 μg/kg) and spiramycin (1539.8 ± 469.4 μg/kg), widely exceeding their legal maximum residue limits (MRLs) established, were detected in milk collected 24 h after treatment, making the cheese production in most cases impossible. After the seven-day period, only spiramycin was detected in goat's milk (79.6 ± 19.2 μg/kg) although no antibiotic residues were found in the cheeses. A withdrawal time of seven days seems suitable to guarantee milk safety after the administration of erythromycin and tylosin without any negative effects neither on the milk nor on the and cheese properties. However, given the rapid elimination of these substances, a shorter withdrawal period might be considered. For spiramycin, persisting in milk for a longer period, further studies on its pharmacokinetics in dairy goats would be recommendable to avoid a potential risk to consumer health.