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Title: HERD AND STATE MEANS FOR SOMATIC CELL COUNT IN DAIRY HERD IMPROVEMENT

Author
item Norman, H
item MILLER, R. - RETIRED, ARS
item Wiggans, George
item Wright, Janice

Submitted to: American Dairy Science Association Proceedings
Publication Type: Abstract Only
Publication Acceptance Date: 6/20/1999
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Some in the dairy industry have advocated reducing the legal limit for somatic cell count (SCC) in market milk from the current level of 750,000 cells/ml. Data from 539,547 herd test days for Dairy Herd Improvement (DHI) herds from 1996 and 1997 were examined to determine the probable impact of such a change. Individual cow lactation records were used to compute herd means on test day. Data available were somatic cell scores that were converted to SCC. An individual cow SCC was weighted by milk yield to calculate herd test day means. Means were derived for each state by 1) equally weighting SCC for each herd test day and 2) weighting SCC by herd test day milk yield. Weighted state means were lowest in the Northeast and West and highest in the South. Percentage of herd test days with SCC > 750,000 cells/ml ranged from 0 to 14% across states (mean of 4%). Of the herds with an SCC test > 750,000 cells/ml, 18% exceeded that level on the next herd test day. Mean SCC in the US was 307,100 and 313,500 cells/ml in 1996 and 1997. Herd size and SCC were negatively related. Therefore, state means calculated by weighting herd test day SCC by yield were lower (17,000 cells/ml) than when herd test day SCC were weighted equally. Mean SCC was lower in October through January (280,000 to 300,000 cells/ml) than in July and August (340,000 cells/ml). Because records of some cows treated with antibiotic were included in the data, SCC means likely were higher than corresponding bulk tank readings. Most herds appeared to be well below the legal bulk tank SCC limit and could meet even lower levels (e.g., the 500,000 cells/ml limit used in some countries). However, some herds exceeding the current limit appear to have the same problem repeatedly. Refinement of economic incentives is a way to reduce this situation.