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Title: Somatic cell counts of milk from Dairy Herd Improvement herds during 2008

item Norman, H
item Ross Jr, Frank

Submitted to: AIPL Research Reports
Publication Type: Government Publication
Publication Acceptance Date: 2/10/2009
Publication Date: 2/18/2009
Citation: Norman, H.D., Miller, R.H., Ross Jr, F.A. 2009. Somatic cell counts of milk from Dairy Herd Improvement herds during 2008. AIPL Research Reports. SCC10 (2-09).

Interpretive Summary:

Technical Abstract: Test-day data from all herds enrolled in Dairy Herd Improvement (DHI) somatic cell testing during 2008 were examined to assess the status of national milk quality. Cows with records failing some AIPL editing procedures were excluded. Somatic cell score (SCS) is reported to AIPL and was converted to somatic cell count (SCC) for calculating herd and State averages. The current legal limit for bulk tank SCC is 750,000 cells/ml for Grade A producers. Nationally, average SCC during 2008 was 262,000 cells/ml. The percentages of herd test days that exceeded 750,000, 600,000, 500,000, and 400,000 cells/ml during year 2006 were 3.4, 7.1, 12.5, and 22.4, respectively. Thus, 3.4% of test-days from DHI herds were higher than the present legal limit for SCC of bulk tank milk. This may overestimate the percentage of herds that would have exceeded the legal limit for bulk tank SCC on test day because the milk of cows treated for mastitis is excluded from the bulk tank but not excluded from the DHI test. Also, the percentage of herd test days exceeding the legal limit would have been higher than the percentage of herds that were rejected from the market because market exclusion only occurs after repeat violations. Variation among States was large. Average SCC's were lower in the far West and higher in the Southeast, Mid-Atlantic, and Central states. SCC differences between adjacent states were substantial, which suggests that mastitis-control regimens have an impact under similar climatic conditions. As herd size increased, average daily milk generally increased, while average SCC declined. Notably, herds with <50 cows had 6.0% of test days over 750,000 cells/ml while in larger herds 0.0 to 1.7% of test days were over this limit. Herd test day averages by month showed that milk yield decline during the summer months. SCC increased from May through July, then decreased from August through November. The highest quality milk was produced in October, November, and December.