"The ideal system for recording clinical mastitis will allow the practitioner to evaluate important cow factors that define the probability of treatment success and assess trends over time," noted Pamela Ruegg, with the University of Wisconsin Quality Milk Group.

To begin involvement in mastitis control programs, Ruegg, presenting at the Minnesota Dairy Health Conference, noted that veterinarians should ensure the following questions can be answered:

1. What is the incidence (rate of new cases) of clinical mastitis?


2. What proportion of cases are severe (severity score of 3)?


3. What are the most common bacteria that are causing clinical mastitis?


4. What are the current treatment protocols?


5. How many days is milk discarded as a result of treatment?


6. How many cases either require changes to the original treatment protocol or experience recurrence of the case within the same lactation?


7. What percent of lactating cows are being milked on less than four quarters?


8. What percent of cows that experience clinical mastitis are culled in the same lactation or die?

Researchers generally define separate cases of clinical mastitis based on an interval of 14 to 21 days between occurrences. This time period is not based on sound research and may be adapted to meet the needs of the farm.

Key performance indicators that are defined at the cow level (occurrence of mastitis in one or more quarters of a cow) rather than the individual quarter are easier to record and may better reflect the important economic consequences of mastitis.

For the incidence rate, Ruegg suggests targeting the following goals:

• Incidence rate of less than 25 new cases per 100 cows per year (about two to three cases per 100 cows per month).
  
• Fewer than 30 percent of cases recurring (two or more treatments).
  
• Less than 20 percent of cows with more than one quarter infected. If the number of cases with more than two quarters affected divided by the total number of cases is greater than 1.4, there could be a mycoplasm issue.
  
• The number of days milk is discarded per case should be between four and six unless cows are receiving extended therapy. This parameter is an indicator of protocol compliance.

In our blog last Thursday, Somatic cells: the best indicator of subclinical infections, we discussed Ruegg's key parameters for assessing subclinical mastitis.

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The author, Amanda Smith, was an associate editor and is an animal science graduate of Cornell University. Smith covers feeding, milk quality and heads up the World Dairy Expo Supplement. She grew up on a Medina, N.Y., dairy, and interned at a 1,700-cow western New York dairy, a large New York calf and heifer farm, and studied in New Zealand for one semester.