In recent years, the dairy industry has enjoyed steady improvements in milking equipment, cow environment, teat dips and genetics. While these improvements are notable, dairy producers are still faced with udder health challenges that range from fine tuning somatic cell counts to the occasional severe mastitis case. These challenges can often be fatal or permanently damaging to the cow.
A case of mastitis is estimated to cost over $100 in direct costs and over $400 when future costs such as production loss and premature culling are considered. (Rollin, Dhuyvetter, Overton – Preventative Veterinary Medicine 2015). Factors that influence the total cost of a mastitis case include rate of contagious transmission, bacteriologic cure rate, herd replacement cost, and decreased milk production. (Down, Green, Hudson – Journal of Dairy Science 2013).
Given the economic importance of mastitis, a strategic approach to clinical and subclinical mastitis is important for every dairy farm. Culturing is considered the gold standard in mastitis diagnostics. By identifying the pathogen involved and considering the cow’s history of past mastitis events or elevations in somatic cell count, we are able to determine the likelihood of cure and the contagious risk to other cattle. The costs to perform these diagnostics are low and the majority of pathogens can be isolated within 24 hours. The following is a brief overview of common mastitis pathogens, their causes, and typical outcomes.

Gram Negative Mastitis Pathogens
Gram Negative mastitis pathogens are environmental pathogens found in manure, bedding, water, soil, and plant materials. Most pathogens in this group respond poorly to antibiotic treatment. Some gram negative bacteria are likely to cure without treatment, while others are more likely to cause chronic and sometimes untreatable infections. For this reason, it is important to differentiate the gram negative pathogens.
E coli: causes acute, frequently toxic, mastitis. Mild cases often cure spontaneously, but severe cases can be fatal.
Klebsiella: causes acute, sometimes toxic, mastitis. This form is associated with wet, organic material. Mild cases often cure spontaneously, but severe cases can be fatal.
Enterobacter: causes acute, sometimes toxic, mastitis. Mild cases often cure spontaneously, but severe cases can be fatal.
Serratia: can be subclinical or clinical. This pathogen has a poor response to antibiotic treatment and the cure may lead to abandoning the quarter or culling.
Pasteurella: causes acute toxic mastitis. This pathogen is unresponsive to antibiotic treatment and can be fatal.
Pseudomonas: causes chronic low grade or acute toxic mastitis. This form thrives in wet environments and does not respond well to antibiotics.
Proteus: a less common cause of acute mastitis that thrives in wet environments and does not respond well to antibiotics.

Of the commercially available mastitis antibiotics, Ceftiofur products have the best gram negative spectrum. Supportive care is an important component of treatment for moderate to severe mastitis cases. This may involve oral or IV fluid therapy, anti-inflammatory treatments, and potential systemic antibiotics.  Some farms elect to withhold intramammary antibiotics for mild cases caused by gram negative mastitis pathogens. Talk to your herd veterinarian about a targeted gram negative protocol, and be sure to monitor outcomes of your decision.

Gram Positive Mastitis Pathogens
Gram Positive mastitis organisms are endemic to the environment and skin of dairy cattle. Characteristics of common gram positive mastitis pathogens are listed below.
Streptococci: These bacteria are typically picked up from the cow’s environment. Strep species represent the most common cause of chronic infections on many dairies and longer duration therapies are sometimes needed.(Strep ag is no longer commonly found in Wisconsin dairy herds, but has a far more acute, contagious presentation).
Coagulase Negative Staphylococci: These bacteria are common skin flora of the teat and udder. Poor teat dipping practices are a common cause. Infections are frequently subclinical resulting in 2-3x increases in SCC. Infections vary in their persistence.
Staph aureus: This is a highly contagious mastitis pathogen that is primarily transmitted from infected quarters during the milking process. The hands of milkers, teat cups, and parlor towels are common means of spreading the pathogen. Staph aureus infections wall off in the mammary gland making treatment less effective than other pathogens. The walled off infections sporadically break open leading to repeated infections and varying cell counts. Culture and culling is a common strategy for fighting Staph aureus issues at the herd level.

All of the commercially available mastitis antibiotics have suitable spectrum for gram positive mastitis cases. Products differ in the duration and interval for which they are researched and labeled. For Streptococcal mastitis, longer duration therapies are frequently necessary to achieve bacteriologic cures. Talk to your herd veterinarian about choosing a product appropriate for your farm’s pathogen profile.

Other Organisms Implicated in Bovine Mastitis
Prototheca: An algae that thrives in wet environments, Prototheca typically causes low grade mastitis with months-long incubation periods before detection. Some Prototheca infected cows do not show elevated cell counts but most will eventually develop a clinical case of mastitis. It can spread from cow to cow in the parlor but herd issues often begin with an environmental source. Because Prototheca does not respond to antibiotics, cows are usually culled or the infected quarter dried.
Mycoplasma: This is a highly contagious mastitis pathogen that spreads from cow to cow in the milking parlor. Respiratory and urogenital infections can also spread through the bloodstream to the mammary gland. Fresh heifers can be infected by way of cross-suckling calves or internal spread of respiratory Mycoplasma infections. Mycoplasma mastitis is not effectively treated by intramammary antibiotics so culling is often recommended. A cow that is being added to the herd should be cultured to prevent the introduction of this pathogen.

Because of these differences in risk factors and treatment outcomes, mastitis culture data can help us design the best possible program to limit the number of new infections. Culture data can also help us choose the best treatment protocols for those that do occur. Operational decisions involving bedding, milking routine, teat dip, drug choice, and culling are made easier based on the knowledge of pathogen factors.

LVC Recommends Culture and Records Analysis to Improve Milk Quality
Request a monthly bulk tank culture. Be sure to share these results with your herd health veterinarian.
Culture individual mastitis cases. To maximize the benefit of these results, log them in Dairycomp or wherever you keep individual cow histories. This information can be very useful should a second case of mastitis occur or when evaluating the cow for other purposes.
If contagious pathogens such as Staph aureus, Prototheca or Mycoplasma are present in your herd, develop a strategy with your herd veterinarian to reduce spread and remove infected cows.
Regularly analyze a combination of DHIA and mastitis culture data to design a program that protects your cows and maximizes farm profitability.

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