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Milk quality in Dairy Herd Information (DHI) herds enrolled in SCC testing improved last year, as the average SCC went from 276,000 cells/ml in 2007 to 262,000 in 2008. This compares to 288,000 in 2006 and 296,000 in 2005.
Most states (41) saw a lower average SCC than the previous year; only eight states experienced a higher average SCC. As in the past, variation among states remained large. State average SCCs were lower than the national average in the far West and higher in the Southeast, Mid-Atlantic and Central states.
The current SCC 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 2008 were 22.4%, 12.5%, 7.1% and 3.4%, respectively. The 3.4% 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 declined. For herds with fewer than 50 cows, the percentage of test days with SCC more than 750,000 was 6.0% of the time. It occurred on only 1.7% and 1.0% of the test days for herds with 50 to 99 and 100 to 149 cows, respectively, and averaged only 0.6% of the test days for the remaining large herds. [See report details.]
