Rethinking Clinical Mastitis Therapy

Jonathan Hess, Lou Neuder* and Phil Sears
Dept. of Lg. Animal Clinical Sciences, MSU & *Green Meadows Dairy

The course of treatment for clinical mastitis varies greatly from farm to farm. In most large herds (500 cows or more), a cow is separated from the production herd if clinical mastitis is detected by abnormal milk. Abnormal milk is an indication of a problem that can occur with or without swelling and fever. Clinical mastitis is brought to the attention of the herdsman who must make the decision to move the cow and place her on treatment. Unfortunately, this is often the point where treatment decisions are based on experience and opinions rather than good scientific guidelines and protocols. In order to implement an effective clinical protocol, it is useful to determine the cause of infection and to implement a treatment protocol that is specific for that type of infection. This can result in reduced use of antibiotic drugs and fewer days of unsalable milk.

Green Meadows Trial
Green Meadows Dairy, located in Elsie Michigan, milking 3200 cows twice a day with excellent facilities was enrolled in a clinical mastitis treatment project from October 2001 to May 2002 (Green Meadows is also enrolled in Alta’s highly respected Alta Advantage young sire testing program).

Culturing Clinical Cows
Milk samples from clinical quarters were collected aseptically and cultured on farm.

Treatment Protocol
Starting in October of 2001, clinical cases were not treated until after the culture results were entered on the cow’s record in Dairy Comp 305. If either E. coli or Klebsiella were identified on culture, the cow was marked “No Treat” and the quarter was monitored. All others were marked “TREAT” and started on antibiotic therapy. In early February, half of the cows that cultured “no growth” were removed from the treatment group while the other half continued the routine treatment protocol. The groups were compared for return to normal milk, days out of production, and quarter loss.

Findings from clinical mastitis culture results (n=496); abbreviations = Strep ag (Streptococcus agalactiae); Strep sp. (Streptococcus species, not agalactiae); Staph sp. (Staphylococcus species, not aureus); E. coli (Eschericha coli) and Klebsiella (Klebsiella species

Findings

• The majority of clinical cases occurred in the first 100 days of lactation with peaks at 25 days and 75 days for Gram-negative bacteria (E. coli and Klebsiella) infections.
• The greatest number (28%) Grampositive bacteria infections (Strep and Staph) were cultured in the first 25 days with the remaining infections occurring throughout lactation.
• When the treatment protocol was changed to limit antibiotic therapy to cows that were culturepositive for Gram-positive bacteria, the number of cows requiring intramammary antibiotics was reduced 80%.
• 55% of the clinical quarters cultured “no growth” and 25% cultured Gramnegative bacteria that did not require intramammary antibiotic
• Very few cows with clinical cases of mastitis were ill or had a fever that required immediate attention.
• When treatment was withheld for 24 hours awaiting the culture results, most clinical signs had resolved and the Gram-negative and “no growth” quarters did not require treatment.
• Cows with no growth that were treated with intramammary antibiotics did not return to normal milk quicker and did not have fewer quarters lost.

Summary
In this study, cows with clinical mastitis that cultured positive for E. coli or “no growth” did not benefit from treatment with intramammary antibiotics and milk was deemed unsalable for longer periods due to milk withdrawal requirements. Currently, these cows with clinical mastitis are identified by culture and monitored for fever. They do not receive antibiotic treatment and are returned to the milking herd when milk is observed normal. Only cows that have cultured streptococcal and staphylococcal intramammary infections are treated with antibiotics. Change in treatment protocol has increased mastitis monitoring, reduced the lost days of production and decreased the amount of antibiotic used without jeopardizing the animal’s health and well-being.

Posted Jan 27th

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