Since the number of subclinical cases that eventually show up as clinical is quite variable, dairymen cannot rely solely on a record of the number of clinical cases to evaluate their control program. Further, this record may actually be deceiving if dairymen expect the adoption of a proven management procedure to result in a rapid reduction in the number of clinical cases. After control procedures are implemented, their effectiveness must be evaluated by a more sensitive indicator than the number of clinical cases and for a long enough time to see a response. All milk contains leucocytes and only a few secretory cells. Higher counts are abnormal.
Leucocytes accumulate at the inflamed site to combat invading bacteria.
While excessive SCC usually indicate an infection, other factors may also increase counts. However, factors such as late lactation, old age and environmental stress elevate SCC only slightly compared with the elevation due to infection. By necessity the testing procedures employed, in most areas, result in accurate counts at or near the regulatory level but are only an estimate of counts below one million. Screening tests on individual quarter samples. To be of value as a management tool, the screening test must be conducted on a regular basis.