Myth

Better to treat too many than not enough

Abstract

Use of antimicrobials in animal agriculture is increasingly scrutinized, and it is important that veterinarians are engaged with farmers to ensure that they are used in a manner that meets evolving societal expectations while maintaining animal well-being and farm profitability. On most North American dairy farms, mastitis is the most common bacterial disease of cows, and is usually treated by farm workers without veterinary supervision. On most farms, treatment of mastitis accounts for the majority of antimicrobial treatments and many cases are treated symptomatically without knowledge of etiology. However, as farmers have adopted modern management practices, the distribution of mastitis pathogens has shifted and varies among farms based on differences in housing and management. On many farms, a large proportion of cases are microbiologically negative when detected, or are caused by pathogens that have high rates of spontaneous cure. Other cases are often caused by bacteria that are intrinsically resistant to available antimicrobials or occur in cows with characteristics that greatly reduce the probability that antimicrobial therapy can result in successful bacterial clearance. When antimicrobials are routinely used to treat mastitis without determining the etiology, approximately 35 to 60% of antimicrobial treatments will be of no-benefit to the cow. In an era when use of antimicrobials on farms is increasingly controversial, this is difficult to justify. To develop appropriate treatment protocols, veterinarians should review the spectrum of action of approved drugs and implement protocols that include options for managing cases that will not benefit from antimicrobial use. When possible, veterinarians should encourage farmers to use culture-based treatment protocols and review the medical history of the cow before administration of antimicrobial treatments. When culture-based protocols are not feasible, veterinarians should recommend use of approved narrow-spectrum intramammary antibiotics for short durations. There is considerable opportunity for veterinarians to promote responsible use of antimicrobials by increasing engagement with farmers in development of mastitis treatment protocols.