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Title: Use of cow culling to help meet compliance for somatic cell standards

item Norman, H
item Wright, Janice

Submitted to: Journal of Dairy Science
Publication Type: Abstract Only
Publication Acceptance Date: 2/24/2011
Publication Date: 6/30/2011
Citation: Norman, H.D., Wright, J.R. 2011. Use of cow culling to help meet compliance for somatic cell standards. Journal of Animal Science 89(E-Suppl. 1)/Journal of Dairy Science 94(E-Suppl. 1):27-28(abstr. M69).

Interpretive Summary:

Technical Abstract: Stricter somatic cell count (SCC) standards are expected in the United States. This study examines the degree to which a single high test increases the risk of non-compliance, and whether culling strategies can help keep the herd in compliance. Source of data was somatic cell scores (SCS) from 14,346 Dairy Herd Improvement (DHI) herds having 15 to 26 tests from Jan. 2009 to Oct. 2010 and >=10 cows for all tests. Cow SCC were derived from cow SCS by SCC = 2(SCS – 3)(100,000). Herd test-day SCC was a proxy for bulk tank SCC and was determined by weighting individual cow SCC by their test-day milk yield. The herd test-day SCC were the basis for determining the percentage of herds that would fail compliance using the current or proposed US standard because 3 of 5 consecutive SCC tests exceeded 750,000, 600,000, 500,000, or 400,000 cells/mL. Oct. 2009, Feb. 2010, and June 2010 were each used as starting points and the probability of being non-compliant 4 mo later was determined. The effectiveness of different culling approaches, e.g., culling high cows based on current SCC, based on an index of previous and current SCC, or culling all those above designated parities (e.g., parity 4 or 5) was examined. Culling cows likely to have high SCC in their next 4 tests was the goal. Various percentages of the cows (1 to 5%) with high SCC were deleted to simulate culling when a herd test exceeded one of the alternative limits. Herd-test-days SCC were recalculated absent these high-SCC cows so the herd compliance rate for the next 4 tests could be recalculated and compared to the rate without simulated culling. When the herd had a high month in Oct. 2009, the probability of being non-compliant (400,000 cells/mL) 4 mo later without culling was 55%. Similar values for Feb. 2010 and June 2010 were 62 and 66%. By culling 5% of the cows with the high SCC, this dropped to 46, 50, and 55%. Culling cows with parity >4 reduced it to 48, 52, and 56% in the same months.