Promoting judicious antibiotic use: On-farm culture-based treatment strategies

Abstract

Traditionally, dairy farmers have treated all cases of clinical mastitis (CM) with antibiotics leading to incorrect or overtreatment of many cases. On-farm culture (OFC) allows rapid detection of pathogen groups allowing for a more targeted approach to treatment. In a Canada- wide clinical trial, cows with mastitis of mild to moderate severity were randomly allocated to either an OFC group or an antibiotic treated control (TC) group. In the OFC group, milk was applied to coliform count and total aerobic count Petrifilms at a 1:10 dilution with sterile water and incubated at 35 °C for 22-24 hours. Cases identified with Gram positive pathogens on OFC were treated with intramammary cephapirin sodium for 2 consecutive milkings. Cows in the TC group were promptly treated with intramammary cephapirin sodium. Milk samples were taken pre-treatment and 14-21 and 28-35 days post-treatment and submitted for standard bacteriologic culture in all cases. Producers recorded the date of mastitis occurrence and the date that milk returned to normal appearance. No difference in clinical cure (P=0.164) was observed between groups. Bacteriologic cure differed between groups which was attributable to false negative diagnosis (P=0.018). Primary antibiotic use was reduced by 40.2% in the culture group with no difference in risk of receiving secondary antibiotic treatment compared to the control group (P=0.588). The 3M Petrifilm culture system shows promise in developing selective treatment strategies for clinical mastitis. Results from this study will be used to educate dairy farmers on the importance of judicious antibiotic use and the benefits of culture-based targeted treatment strategies.