Antibiotic treatments for bovine mastitis

Who, what, when, how and why?

Abstract

Mastitis is the most common disease of dairy cattle, and control of this disease is responsible for the majority of antimicrobials administered to adult dairy cows. Mastitis is detected subsequent to initiation of the immune response based on recognition of inflammation. Thus, most cases present with mild or moderate symptoms, and many cases are culture-negative. Most mastitis is treated by milking technicians without diagnosis of the etiology or review of the medical history of the cow. Obtaining a microbiological diagnosis is essential because some cases may spontaneously cure or respond to short-duration therapy, some cases may require longerduration therapy, some cases are culture-negative, and some cases are caused by pathogens for which there are no effective approved antimicrobials. Practitioners have an opportunity to reduce antimicrobial usage and improve mastitis treatment protocols by targeting treatments based on etiology and cow characteristics. Veterinarians should monitor selected outcomes after treatment and design treatment protocols based on etiological agents specific to individual cases or farms. Milking personnel should be trained to detect abnormal milk and aseptically collect milk samples, but treatment protocols should be performed by animal health managers based on etiology and review of the animal health history. The ability to achieve bacteriological cure is strongly associated with etiology and history of previous cases occurring in the affected cow. The need for antimicrobial therapy and the duration of treatment depend primarily on characteristics of the agent and the ability of the cow to initiate a strong immune response. Bacteria that have the ability to invade secretory tissue, such as Staphylococcus aureus, many environmental streptococci, and many strains of Klebsiella spp typically respond better to extended-duration therapy. In contrast, pathogens that infect superficial mucosal surfaces, such as coagulase-negative staph, Streptococcus agalactiae, and most strains of Escherichia coli) are typically cured with short-duration therapy. Producers should be trained to review the somatic cell count history of the cow and use that data to direct treatment decisions. Cows with a longer duration of subclinical infection prior to the clinical case are more likely to require antimicrobial therapy. The decision to administer antimicrobials should be based on determination of etiology by use of rapid-culture systems used either on-farm or in veterinary clinics. Many mild and moderate clinical cases that are culture-negative and detected in otherwise healthy cows can be successfully managed using a strategy of watchful waiting. Cows that are chronically affected and have frequent recurrences should not be repeatedly dosed with antimicrobials, but should either be culled or have the affected glands therapeutically dried off.