Use of cow culling to help meet compliance for somatic cell standardsH. 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 >5th 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 >4th 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 & METHODSMilk 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 + b1DIM + b2DIM2 + b3SCCcurrent_mo +b4SCCcurrent_mo-1* + b5SCCcurrent_mo-2* +b6SCCprevious_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

Percent of herds exceeding SCC standard in October 2009October 2009 that were noncompliant in February 2010

Percent of herds exceeding SCC standard in February 2010February 2010 that were noncompliant in June 2010

Percent of herds exceeding SCC standard in June June 2010 2010 that were noncompliant in October 2010

Herd size (cows)

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RESULTS (cont.)

SCC standard (cells/mL)

400,000 500,000 600,000 750,000

Culling method % noncompliant in June 2010No additional culling 61.5 50.2 40.2 35.0

1% - current score 55.8 45.4 36.5 30.11% - prediction model 57.2 45.4 34.9 30.75% - current score 50.1 39.4 31.2 26.95% - prediction model 51.4 40.1 31.2 29.010% - current score 43.2 32.2 25.4 19.910% - prediction model 44.0 33.7 25.4 23.7

All cows above parity 5 56.0 45.8 35.8 29.6All cows above parity 4 52.6 40.6 31.9 26.3

SCC standard (cells/mL)

400,000 500,000 600,000 750,000

Culling method % noncompliant in October 2010No additional culling 66.2 55.2 46.2 37.9

1% - current score 61.7 50.4 41.7 35.01% - prediction model 61.4 49.6 41.2 35.05% - current score 54.9 44.2 37.2 33.95% - prediction model 56.0 44.7 37.4 31.110% - current score 47.2 37.3 31.1 29.910% - prediction model 48.2 36.5 32.0 26.6

All cows above parity 5 61.7 50.5 43.0 35.6All cows above parity 4 56.4 44.9 38.5 32.8

•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)

•Percent of herds exceeding SCC level of 400,000 cells/mL in June 2010June 2010 that were noncompliant in October 2010 by culling method and herd size

October 2009

February 2010

June 2010

SCC standard (cells/mL)

2011

SCC standard (cells/mL)

400,000 500,000 600,000 750,000

Culling method % noncompliant in February 2010No additional culling 55.2 44.7 36.0 29.9

1% - current score 50.5 40.7 33.0 27.71% - prediction model 51.2 39.8 32.1 27.05% - current score 46.2 36.4 30.8 24.15% - prediction model 46.5 37.0 29.4 24.110% - current score 38.1 30.4 25.8 20.410% - prediction model 40.3 31.4 24.7 19.7

All cows above parity 5 52.4 40.3 32.1 27.7All cows above parity 4 47.6 37.4 29.9 24.1