1. Use of cow culling to help meet compliance for somatic cell standards H. D. Norman and J. R. Wright * Animal Improvement Programs Laboratory, Agricultural Research Service, USDA, Beltsville, MD 20705-2350 Abstr. M69 INTRODUCTION  Stricter SCC standards have been proposed by various US dairy organizations that could drastically increase the number of herds facing noncompliance penalties.  Some milk processors have already begun adjusting their standards to comply with requirements necessary for export to the European Union.  Dairy producers not meeting the more rigorous SCC standards may need to apply management and culling changes to achieve compliance.  To assess the extent that cow culling could be used in helping to achieve SCC compliance if standards change  Compare various simulated culling strategies to determine which would be most effective in meeting SCC compliance levels CONCLUSIONS  Culling was only moderately successful in helping herds with high SCC herd averages achieve compliance.  Culling based on the prediction model had no advantage over culling based on a single month’s SCC in improving herd compliance.  Culling >5 th parity cows resulted in removing 5-7% of animals in affected herds, yet only improved compliance levels similar to culling 1% based on a single month SCC score.  Similarly, culling >4 th parity cows removed 10-15% of cows, yet yielded compliance equivalent to culling 5% based on monthly score.  Culling improved compliance more when the SCC standard was lowest (400,000) than at the current standard (750,000), regardless of culling method.  An earlier study found that a larger percent of small herds were noncompliant compared to large herds. For herds exceeding SCC levels in the initial month, herds of all sizes benefited from culling.  Percent of herds noncompliant after 4 additional tests was higher in October 2010 than in February or June 2010 for all SCC standards. http://aipl.arsusda.gov OBJECTIVES DATA & METHODS  Milk and somatic cell scores (SCS) were from the US national dairy database for 14,854 Dairy Herd Improvement Association (DHI) herds that had 15 to 26 tests between January 2009 and October 2010  Individual cow SCC calculated as: SCC = 2 (SCS-3) x (100,000)  Herd test-day SCC was derived by weighting each individual cow’s SCC by test day milk yield  Herd compliance was determined for individual months (October 2009, February 2010, June 2010)  Culling strategies were simulated for herds exceeding the SCC limit in the initial month by removing records of designated cows from their subsequent month’s herd SCC average  Compliance was examined using the next 4 tests, simulating the US testing method requiring at least 3 of 5 consecutive months at or below proposed standards of 400,000, 500,000, 600,000, and the current level, 750,000 cells/mL. DATA & METHODS (cont.) Culling strategies: 1. In herds exceeding SCC standard in the initial month, cull 1, 2, 3, 4, 5 or 10% of cows with the highest initial month’s SCC score 2. Same as above but select cows to cull based on a prediction model for SCC score: Predicted SCC = herd + parity + month + b 1 DIM + b 2 DIM 2 + b 3 SCC current_mo +b 4 SCC current_mo-1* + b 5 SCC current_mo-2* +b 6 SCC previous_parity* + error *When cow has no previous test or parity, herd-parity SCC average used 3. In herds exceeding SCC standard in the initial month, cull all cows above a selected parity (4 or 5) RESULTS (cont.) RESULTS October 2009 Percent of herds exceeding SCC standard in October 2009 that were noncompliant in February 2010 February 2010 Percent of herds exceeding SCC standard in February 2010 that were noncompliant in June 2010 June 2010 Percent of herds exceeding SCC standard in June 2010 that were noncompliant in October 2010 Herd size (cows) Percent noncompliant RESULTS (cont.) SCC standard (cells/mL) 400,000500,000600,000750,000 Culling method% noncompliant in June 2010 No additional culling61.550.240.235.0 1% - current score55.845.436.530.1 1% - prediction model57.245.434.930.7 5% - current score50.139.431.226.9 5% - prediction model51.440.131.229.0 10% - current score43.232.225.419.9 10% - prediction model44.033.725.423.7 All cows above parity 556.045.835.829.6 All cows above parity 452.640.631.926.3 SCC standard (cells/mL) 400,000500,000600,000750,000 Culling method% noncompliant in October 2010 No additional culling66.255.246.237.9 1% - current score61.750.441.735.0 1% - prediction model61.449.641.235.0 5% - current score54.944.237.233.9 5% - prediction model56.044.737.431.1 10% - current score47.237.331.129.9 10% - prediction model48.236.532.026.6 All cows above parity 561.750.543.035.6 All cows above parity 456.444.938.532.8 Percent of herds above SCC standard for selected month (solid) and percent that would be noncompliant after 4 additional tests with no change in culling (shaded) June 2010 Percent of herds exceeding SCC level of 400,000 cells/mL in June 2010 that were noncompliant in October 2010 by culling method and herd size October 2009 February 2010 June 2010 SCC standard (cells/mL ) Percent of herd s 2011 SCC standard (cells/mL) 400,000500,000600,000750,000 Culling method% noncompliant in February 2010 No additional culling55.244.736.029.9 1% - current score50.540.733.027.7 1% - prediction model51.239.832.127.0 5% - current score46.236.430.824.1 5% - prediction model46.537.029.424.1 10% - current score38.130.425.820.4 10% - prediction model40.331.424.719.7 All cows above parity 552.440.332.127.7 All cows above parity 447.637.429.924.1