Somatic cell count (SCC) in Dairy Herd Improvement (DHI) herds enrolled in SCC testing averaged 233,000 in 2009, which was considerably less than the 2008 average of 262,000. This compares to 276,000 in 2007; 288,000 in 2006; and 296,000 in 2005.

Most states (42) had lower average SCC than the previous year; only six states had higher averages. Variation among states remains large, ranging from less than 200,000 to more than 400,000. State average SCC was lower than the national average for mountain and western states, and often higher for southeastern states.

The current federal SCC regulatory limit in the U.S. is 750,000, except in California where it is 600,000. In many other major dairy countries, the SCC limit is 400,000.

The overall percentage of herd test days that exceeded 400,000, 500,000, 600,000, and 750,000 during 2009 were 18.9 percent, 10.3 percent, 5.8 percent and 2.7 percent, respectively. (The 2.7 percent figure may overestimate the percentage of herds with milk exceeding the legal limit for bulk tank SCC on test day, because the milk of cows treated for mastitis is included in DHI test data, but is excluded from the bulk tank.)

As herd size increased, average daily milk production generally increased and average SCC generally decreased. The percentage of test days with SCC more than 750,000 in herds with fewer than 50 cows was 5.0 percent. This compares to 1.4 percent for herds with 50 - 99 cows; 0.7 percent for herds with 100 - 149 cows; and only 0.3 percent in herds with 150 or more cows.

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Source: NMC (formerly the National Mastitis Council)