An on-farm culture system as a tool to reduce the use of antimicrobials on commercial dairy farms

Clinical mastitis is defined as an inflammatory reaction of the udder tissue to bacterial infection resulting in characteristic signs of mammary gland inflammation . Antimicrobial drugs are usually used for the treatment of such infections. In the past few decades, a shift in the etiology of clinical mastitis from Gram-positive bacteria to Gram-negative bacteria, including cases with no bacterial growth, has been reported. Gram-negatives and no growth cases were associated with over 50% of mastitis cases (Lago et al. 2011). The question is whether the use of antibiotics for treatment of mild to moderate Gram-negative infections such as coliform mastitis has some benefits because the spontaneous cure rate is high (Wilson et al., 1999). On the other hand, mastitis caused by Gram-positive bacteria requires a different approach from mastitis caused by Gram-negative bacteria and the use of antibiotics in such cases is routinely recommended. Therefore, rational mastitis therapy requires knowledge of the etiological agent before making a decision about treatment.

In addition, there is an increasing public concern that the overuse of antibiotics in agriculture may lead to antimicrobial resistance in humans. Thus the routine use of broad spectrum antibiotics without identification of the causative