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United States Department of Agriculture

Agricultural Research Service

Title: Herd and State Means for Somatic Cell Count for Dairy Herd Improvement

Authors
item Norman, H
item Miller, Robert - RETIRED, ARS
item WRIGHT, JANICE
item WIGGANS, GEORGE

Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: June 7, 2000
Publication Date: N/A

Interpretive Summary: Milk SCC is a barometer of milk quality and an elevated SCC is an indicator of mastitis. To ensure high quality dairy products, bulk tank SCC (BTSCC) is monitored in milk from Grade A producers. A shipment > 750,000 cells/ml triggers a process by which a producer's milk may be excluded from the market if the limit continues to be exceeded in subsequent tests. Also, additional premiums are paid for milk with low BTSCC. Databases with BTSCCs are not readily available. SCC from DHI herds may help fill this void. To determine the impact of reducing the current legal limit of 750,000 cells/ml for SCC in US market milk, as has been proposed, data were examined from 539,577 herd test days for Dairy Herd Improvement herds on milk recording throughout 1996 and 1997. Somatic cell scores for individual cows were converted to SCC. Regional differences in SCC were large. State means were lowest in the West and highest in the South. Percentage of herd test days with an SCC of > 750,000 cell/ml ranged from 0 to 14% across states; the mean was 4%. Only 1% of the herd's tests were > 750,000 cells/ml on two consecutive test days. Year differences were present. Seasonal differences in herd means for test day SCC were as expected; SCC were highest in summer and lowest in winter. Herd size and SCC were negatively related; larger herds had lower SCC. Most herds had test day SCC that were substantially below legal bulk tank limits and could have met lower limits. Statistics on the probability of herds producing milk which meet lower SCC limits of 600,000, 500,000, and 400,000 cells/ml were provided. Greater efforts to improve milk quality are needed. Placing more emphasis on price incentives to reward the production of quality milk might be a solution.

Technical Abstract: To determine the impact of reducing the current legal limit of 750,000 cells/ml for somatic cell count (SCC) in US market milk, data were examined from 539,577 herd test days for Dairy Herd Improvement herds on test during 1996 and 1997. Somatic cell scores for individual cows were converted to SCC. The SCC for each cow was weighted by milk yield and used to compute herd mean on test day. The mean for each state was derived by weighting herd test day SCC by herd test-day milk yield. State means were lowest in the West and highest in the South. Percentage of herd test days with an SCC of >750,000 cells/ml ranged from 0 to 14% across states; the mean was 4%. Only 1% of the herds tests were >750,000 cells/ml on two consecutive test days. Mean SCC in the US was 307,100 cells/ml for 1996 and 313,500 cells/ml for 1997. Mean SCC was lower during October through January (280,000 to 300,000 cells/ml) than during July and August (340,000 cells/ml). Herd size and SCC were negatively related; larger herds had lower SCC. Because records of some cows treated with antibiotics were included in the data, SCC means likely were higher than corresponding bulk tank SCC. Most herds had test day SCC that were substantially below legal bulk tank limits and could have met lower limits (e.g., 500,000 cells/ml).

Last Modified: 9/10/2014
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