Qualitative survey on antibiotic use for mastitis and antibiotic residues in Umbrian dairy herds

Antibiotics still represent one of the strategies to fight, to prevent and to control mastitis in dairy cattle, however they can lead to the rise of antibiotic-resistance and the presence of pharmaceutical residues. Two approaches were used to obtain data about these topics. A qualitative survey was conducted to better understand the use of antibiotics to treat mastitis in Umbrian dairy herds, using an appropriate questionnaire. The analysis of the answers showed that good farming and milking practices were significantly linked with a more rational use of antibiotics. Moreover, checks conducted by breeders associations had a positive influence on farm management and so were associated with a more responsible use of antimicrobials. For the other aim, residues in bulk milk and in the milk of individual cow treated with antibiotics for mastitis were monitored using a microbiological screening test and a liquid chromatography/high resolution mass spectrometry (LC-HRMS) confirmatory method. Broad-spectrum penicillins, fluoroquinolones, macrolides and cephalosporins were the classes of antibiotics most widely used during lactation, whereas 1st generation cephalosporins were used most in dry periods. Samples from 748 bulk milk tanks from 30 dairy herds were assayed and no suspect samples were found. This could be due to the fact that the tank milk was diluted or that antibiotics for mastitis had been correctly managed. Two samples from a cow treated with procaine benzylpenicillin + dihydrostreptomycin were positive during the screening and 1600 mu g/kg and 1100 mu g/kg of dihydrostreptomycin were determined respectively by LC-HRMS. These positive results might be indicative of either the uniqueness of the tested animal's metabolism or the improper use of antibiotics. Monitoring antibiotic use in Italian regions is necessary to quantify the risk both of residues in milk and of the selection of drug-resistant bacteria and it could stimulate a more rational and responsible use of antibiotics.