Simply the Facts - SCC and SCS

U.S. national standards for SCC are 750,000 cells/ml, with the exception being the State of California's limit of 600,000. Globally, most other major dairy producing countries have a limit of 400,000.

Starting October 1, 2010, all dairy processors who export products to the EU need to certify all milk originates from farms with a rolling three-month geometric mean¹ SCC below 400,000. Previously, processors could co-mingle milk from different farm sources to meet this standard.

Average SCC for U.S. farms was 233,000/ml in 2009, and the U.S. herd statistics show a constant downward trend since 2005. The overall percentage of herds that exceeded 400,000 during 2009 was 18.9 percent.

Industry estimates indicate losses of approximately $200 per cow per year due to reduced milk production, treatment costs, discarded milk and reduced milk quality premiums. Hidden costs of mastitis include decreased genetic advancement as well as premature culling and death.

SCC is shown on a log score, or per every 1,000 cells/ml. SCS is a uniform linear score of SCC as shown below.

USDA-AIPL² routinely publishes sire rankings for predicted transmitting ability for SCS. These rankings provide producers an opportunity to select bulls on their ability to sire daughters with lower rates of subclinical and clinical mastitis.

The average SCS is +3.00 for all bulls of all breeds. Bulls with SCS values below +3.00 are expected to sire daughters with lower SCC and less mastitis. In reverse, bulls with SCS above +3.00 will likely sire daughters with higher SCC and a greater incidence of mastitis. Industrywide, the approximate range for SCS is +2.40 to +3.50.

High production and more frequent rates of mastitis are genetically correlated. Therefore, if you select only bulls with low SCS, you will likely not be selecting for high rates of improved milk yield. It is a tricky balancing act to optimize milk yield and breed for lower SCS. Fortunately, the Lifetime Net Merit (LNM) index takes into account both the value of a bull's PTAs for yield traits and SCS. SCS receives a 10 percent weighting within the LNM formula.

Cows with high SCS tend to have greater difficulty achieving pregnancy. Thus, bulls with high SCS often have very low PTAs for Daughter Pregnancy Rate. On a positive note, there is a very strong favorable correlation between SCS and udder depth with shallow udders leading to lower SCS.

While nothing can replace the role of management and preventative care in controlling mastitis, selection of bulls based on LNM with reduced SCS places emphasis on optimal yield and udder conformation.