An often quoted line from the business world is “if you can measure it, you can manage it”. Dairy farms by their nature are complex businesses where not all aspects of the operation can be easily measured. We are fortunate though that the measurement tools for milk quality are readily available and very interpretable. 
 
In the October newsletter we described the benefits of lowering bulk milk somatic cell count (BMSCC). BMSCC is an excellent example of a farm performance measurement with very high frequency. Movement in BMSCC can be used to obtain an approximate estimate of change in subclinical mastitis infections in the herd. It makes intuitive sense that if the BMSCC is rising, as a general herd trend, the proportion of the herd sub-clinically infected is potentially increasing. Care does need to be taken in seasonal calving herds however, as the change in BMSCC also needs to be interpreted relative to any reduction in milk volume over the month (or months) as the measure is in cells/ml. Recall that a sudden, between pick-up increase in BMSCC of 50,000 or more can be a signal that a clinical case has been missed in the herd. 
 
The recording of clinical mastitis cases is required for multiple quality assurance and farm management reasons; If these cases are not recorded correctly, it becomes more difficult to manage cows that should be withheld from supply. The clinical mastitis records from this season, and the last, can also become one of the key indicators of new mastitis infection rate. If the clinical mastitis rate in cows in their first 14 days in milk is greater than 8 cases/100 cows, then this is a “trigger” to indicate an elevated new infection rate worthy of investigation. Similarly, for cows beyond 15 days in milk, if the clinical mastitis rate is greater than 1 cow/100 cows/month then this too is an indication that the new infection rate should be investigated. Total clinical cases for the herd should be under the trigger level of 15% of cows affected per season. These triggers are all described in Smart SAMM resources. 
 
Where herd testing is used, changes in the proportion of cows greater than the threshold indicating a likely subclinical infection (150,000 cells/ml for cows and 120,000 cells/ml for heifers) between herd test periods, gives us an excellent indication of new infection rate. This is especially the case when changes in this proportion are assessed in first lactation heifers. Causes for an elevated new infection rate should be explored if the trigger of 10 new subclinical infections/100 cows/month is exceeded or where more than 30% of heifers have an ICCC greater than 120,000 at the end of the season. 
 
In any herd, it is impossible to stop all new infections. It is however, very doable to assess new mastitis infection rate using clinical mastitis, herd test and BMSCC records as described. The farm business becomes empowered to take action to reduce new infection risk, where appropriate. Very little additional effort is required to extract value from these farm records and mitigate milk quality risk in the process.