Submitted to: Journal of Dairy Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/1/2011
Publication Date: 12/1/2011
Citation: Norman, H.D., Lombard, J.E., Wright, J.R., Kopral, C.K., Rodriquez, J.M., Miller, R.H. 2011. Consequence of alternative standards for bulk tank somatic cell count of dairy herds in the United States. Journal of Dairy Science. 94(12):6243-6256. Interpretive Summary: Consideration of changes for US standards for bulk-tank somatic cell count (BTSCC) are underway due to a European Union announcement that its standards will be enforced on any herds supplying them imports. For herds participating in Dairy Herd Improvement (DHI) testing or shipping milk to 4 Federal Milk Orders, noncompliance was 0.9% and 1.0%, respectively based on US standards of 750,000 cells/mL and 7.8% and 16.1% for European Union standards at 400,000 cells/mL. Changes in US BTSCC standards proposed without improved herd management would increase noncompliance in DHI and Milk Order herds up to 14.1% and 23.3%, respectively.
Technical Abstract: Comparison of dairy operations failing compliance with current US and European Union (EU) standards for bulk-tank somatic cell count (BTSCC) as well as BTSCC standards proposed by 3 national organizations were evaluated using 2 populations of US dairy herds: Dairy Herd Improvement Association (DHI) herds and herds supplying milk to 4 Federal Milk Orders (FMO). Herds with 15 to 26 mo of data from the period January 2009 through October 2010 were included in the study. Somatic cell scores (SCS) from 14,854 herds and 164,794 herd-tests were analyzed for DHI herds having >=10 cows for all tests. Herd test-day SCC was derived as a proxy for BTSCC and was the basis for determining noncompliance and the percentage of the milk supply they represent. For FMO herds, actual milk marketed and BTSCC were available from >27,000 herds and >325,000 shipments. A herd was noncompliant for the current EU BTSCC standard after 4 consecutive rolling 3-test geometric means (geometric method) were >400,000 cells/mL. A herd was noncompliant for US SCC standards after 3 of 5 consecutive monthly BTSCC shipments (frequency method) were >750,000 cells/mL. Alternative levels proposed (>600,000, 500,000, or 400,000 cells/mL) were examined as well using these 2 methods. A third alternative declared noncompliance when a single 3-mo geometric mean >550,000 or 400,000 cells/mL and a subsequent test exceeded the same level. Results were examined by month and herd size or milk shipped. Noncompliance, using current US standards for the 12 mo period ending October 2010 in DHI and FMO herds was 0.9% and 1.0%, respectively, compared with 7.8% and 16.1% noncompliance with current EU standards. Use of the frequency method always resulted in more noncompliant herds compared with the geometric method. Noncompliance was inversely related to herd size or milk shipped. Using the frequency method at 400,000 cells/mL, noncompliance was triggered on 19.1% of DHI herd-tests in herds with <50 cows compared with 1.1% of those from herds with >=1,000 cows. For FMO herds shipping <900 metric tons, 44.5% of herds triggered noncompliance using the frequency method at 400,000 cells/mL compared with 8.0% from herds marketing >9,000 metric tons. All methods proposed increased the percent of herds and milk exceeding the regulatory limit. Thus producers would need to place more emphasis on reducing mastitis and increase culling on SCC to meet any of the new standards proposed.