What have we learned about S. aureus mastitis in the past 50 years?

Hoard's Dairyman: 

What have we learned about S. aureus mastitis in the past 50 years?

Date: 
Tue, 07/30/2013

Extensive research conducted five decades ago still serves as the basis for milking practices today.

by Abby (Huibregtse) Bauer, Hoard's Dairyman Associate Editor

Staphylococcus aureus (S. aureus) is a Gram-positive, facultatively anaerobic, nonmotile, nonsporulating, catalase-positive, coagulase-positive coccus. What we need to know on the farm level is that it is regarded as the leading cause of contagious mastitis in North America.

In the 1960s, extensive research on S. aureus mastitis was released, and this information set the stage for the understanding and control mechanisms we use today. This work was the basis for the National Mastitis Council’s 10-point mastitis control plan, which has led to a reduction of S. aureus on many farms.

John MiddletonHave we learned anything more about S. aureus mastitis in the last 50 years? That is the question that John Middleton, associate professor from the University of Missouri College of Veterinary Medicine, tackled at the National Mastitis Council regional meeting in Portland, Maine last week.

S. aureus enters the mammary gland through the teat. The mode of transmission from cow to cow most often occurs at the time of milking, through milking unit liners. Prevention is best, and since the 1960s, milking time hygiene has remained the critical control point in preventing infection. Milking equipment maintenance, prescreening heifers and purchased animals for S. aureus, and segregating and milking infected cows last all help prevent the spread of this infectious disease.

When infections occur, treatment options for S. aureus mastitis include intramammary antimicrobial therapy, systemic antimicrobial therapy and vaccination. Research has found cure rates to be between 3 and 74 percent, depending on treatment product, length of treatment and time of administration. Cure success is also impacted by age, somatic cell count (SCC), chronicity of infection, bacteria count and number of infected quarters.

In some parts of the country, S. aureus intramammary infections in prepartum heifers can exceed 30 percent. Again, the infection enters through the teat end. Horn flies are capable of transmitting the disease, and research shows that farms with effective fly control are at lower risk for cases of heifer mastitis than farms without. Farms that purchase replacement heifers have been found to be at higher risk for more cases and new strains of S. aureus than closed herds that raise their own replacements.

Extensive research has been done on the antibiotic intramammary treatment of prepartum heifers. Research shows that cure rates can be quite promising, but the impact of such treatment on first lactation production or SCC varies from herd to herd and shows no benefit in some herds.

To answer the earlier question, we have learned more about S. aureus in the past 50 years. Interestingly though, Middleton explained that current research still supports the basic premise of milking time hygiene as a critical control point in prevention. New technologies will give farms more tools to recognize infected cows earlier, identify strains and track treatment success rates. Research of this economically damaging disease will continue for the next 50 years, but ultimately, managing S. aureus will likely still come down to cow cleanliness and milking procedure at the farm level.


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The author is an associate editor and covers animal health, dairy housing and equipment, and nutrient management. She grew up on a dairy farm near Plymouth, Wis., and previously served as a University of Wisconsin agricultural extension agent. She received a master’s degree from North Carolina State University and a bachelor’s from University of Wisconsin-Madison.

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