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Title: Somatic cell counts of milk from Dairy Herd Improvement herds during 2009

Author
item Norman, H
item MILLER, R - Retired ARS Employee
item Cooper, Tabatha

Submitted to: AIPL Research Reports
Publication Type: Government Publication
Publication Acceptance Date: 2/1/2010
Publication Date: 2/1/2010
Citation: Norman, H.D., Miller, R.H., Cooper, T.A. 2010. Somatic cell counts of milk from Dairy Herd Improvement herds during 2009. AIPL Research Reports. SCC11 (2-10).

Interpretive Summary:

Technical Abstract: Test-day data from all herds enrolled in Dairy Herd Improvement (DHI) somatic cell testing during 2009 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 2009 was 233,000 cells/ml. The percentages of herd test days that exceeded 750,000, 600,000, 500,000, and 400,000 cells/ml during year 2009 were 2.7, 5.8, 10.3, and 18.9, respectively. Thus, 2.7 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 generally lower in the Mountain and Western States and often higher in the Southeastern 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 5.0% of test days over 750,000 cells/ml while in larger herds <1.4% 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 April through July, then decreased from July through November. The highest quality milk was produced in November and December.