Treatment of Clinical Mastitis

Historic and New Perspectives

Abstract

Mastitis continues to be of great importance to the US dairy industry. When diseases on dairy farms were recently evaluated according to effects on productivity, international trade, animal welfare, and zoonotic risk, mastitis ranked highest, above salmonellosis, paratuberculosis, and bovine virus diarrhea.¹ Subclinical mastitis caused by contagious mastitis pathogens still causes substantial economic loss on some US dairy farms, but it can readily be controlled by dry cow antibiotic therapy, hygiene practices in the milking parlor, and selective culling. In herds that have achieved contagious mastitis control, clinical mastitis caused by opportunistic pathogens in the environment or on teat skin is the predominant form of the disease.^2,3 Because these pathogens are ubiquitous, eradication of clinical mastitis is an unreasonable goal. Rather, dairy producers must strive to reduce the incidence of clinical mastitis by instituting hygienic practices that minimize exposure of teats to pathogens and by optimizing immune function through proper nutrition and vaccination. When clinical mastitis develops, as it does at an annual incidence rate of < 5% to > 50%,⁴ veterinarians and dairy producers must make appropriate treatment decisions.

Despite decades of treating clinical mastitis, controversy still exists about when and how to treat it, particularly in herds that have controlled contagious pathogens. The predominant mastitis-causing pathogens in those herds are coliform bacteria, Streptococcus spp. other than Streptococcus agalactiae (environmental streptococci), and Staphylococcus spp. other than Staphylococcus aureus.^2,3 An ideal treatment regimen would be one that is safe, reduces pain and suffering, is efficacious (resulting in rapid clinical and bacteriological cure), causes short milk and slaughter withholding times, avoids unnecessary drug use or excessive labor, positively impacts milk production and survivability, and is economical. Almost certainly the ideal regimen would differ for mild, moderate, and severe episodes of clinical mastitis and episodes caused by different pathogens.  Hundreds of different treatments for clinical mastitis are used daily on US dairy farms, but, in general, even the most common treatments have not been studied in controlled clinical trials to determine if they are better than no treatment at all. In the remainder of this paper, I will discuss some of the common treatments for clinical mastitis in herds that have controlled contagious mastitis, and suggest areas for future study.