DHI test-day SCC averages decline again

USDA’s Animal Improvement Programs Laboratory released its annual assessment of Dairy Herd Improvement (DHI) somatic cell test-day results. 

Nationally, average test-day herd SCC during 2012 was 200,000 cells/milliliter (cells/mL), down 17,000 cells/mL from 2011. Average test-day herd SCC has declined every year since 2005 and every year except one since 2001. 

Forty-two states had lower average SCC than reported in 2011; 5 states had higher averages (Arizona, Louisiana, North Carolina, Rhode Island and Texas). One state, Louisiana, had an average test-day SCC above 400,000 cells/mL.

The current legal limit for bulk tank SCC is 750,000 cells/mL for Grade A producers. Lowering the limit to a maximum of 400,000 cells/mL has been proposed in the past, and will be again at the upcoming National Conference on Interstate Milk Shipments (NCIMS), to be held April 19-24, in Indianapolis, Ind.

Three proposals have been offered for consideration this year, including one from the National Milk Producers Federation (NMPF) that would lower the maximum to 600,000 cells/mL on Jan. 1, 2014 and 400,000 cell/mL on Jan. 1. 2015. For information on the NCIMS, visit www.ncims.org/index.htm.

Variation among states remains large. State average SCC generally was lower than the national average for Mountain and Western states, and often higher for a few Southeastern states. Although climatic conditions (temperature and humidity) surely contributed to regional SCC differences, differences between adjacent states were substantial, suggesting that herd size and mastitis-control practices are impacting state differences as well.

About 1.5% of herd test days exceeded 750,000 cells/mL; 3.3% exceeded 600,000 cells/mL; 6.1% exceeded 500,000 cells/mL; and 12.0% exceeded 400,000 cells/mL.

However, the 1.5% of 2012 DHI herd test days that were higher than the present legal limit for bulk tank SCC may overestimate the percentage of herds that shipped milk exceeding the legal limit because milk of cows treated for mastitis is excluded from the bulk tank even though included in DHI test data. The percentage of herd test-days that exceeded the legal limit also would have been higher than the percentage of herds that were rejected from the market because market exclusion only occurs after repeated violations.

The USDA analysis also looks at SCC based on herd size and by month. In general, larger herds had lower SCC;  SCC increased from May through August and then declined quickly from September through November. The highest quality milk was produced in November and December.

To see the full report, visit http://aipl.arsusda.gov/publish/dhi/current/sccx.html