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Somatic Cell Count (SCC)

Somatic Cell Count (often called SCC, or just "cell count"), is a commonly used measure of udder health and milk quality.

Somatic cells are primarily white blood cells, but can also include some epithelial cells naturally shed from the udder lining. The presence of somatic cells in milk is a natural part of the cow’s immune system.

Low levels are normal, reflecting the underlying physiological process of cell renewal within the udder. Elevated counts indicate the presence of an infection that may need management or treatment.

SCC counts can be measured in the bulk milk tank (BMSCC), or in individual cows (ICSCC)

Normal SCC Counts

SCC includes epithelial cells from the lining of the udder, and the white blood cells which form a key part of the natural immune response to infection.

In a healthy udder, epithelial cells from the lining are naturally shed during the process of milk production and these cells will be detectable in the milk. Evidence suggests that an uninfected quarter has, on average, a SCC of around 70,000 cells/mL (1). Allowing for natural variation based on age, parity, and lactation cycle, it is generally accepted that an SCC below 100,000 cells/mL (2) is reflective of a baseline level in a healthy udder.

Levels between 100,000 and 200,000 cells/mL may indicate extra attention required to a cows udder health (3). The 'cut off' point at which a subclinical infection is considered likely is debated, with a lower threshold potentially having a better chance of identifying all the cows with an infection, but at the risk of also identifying some that do not. This means caution is advised in relying purely on a single data point - a more holistic view of the ICSCC data across a season, follow-up culture testing data, and advice from a vet are all useful in guiding management choices.

High SCC Counts

When an infection or inflammation is present in the udder, the cow’s immune system directs somatic cells, most importantly white blood cells, to the site to attack and destroy any pathogens causing the infection. This is a natural and normal immune response.

A generally accepted threshold for SCC, above which a subclinical infection is considered highly likely and action is warranted is 150,000 to 200,000 cells/mL (2,3,4) , although both higher and lower limits are advocated by some.

When an individual cow SCC count at this level is detected, diagnostic testing can identify the type of bacteria present, and therefore the most suitable course of action treatment or management for the health of that cow, and for the health of the herd.

Cows with persistent infections of Staph. aureus in particular are considered important to identify, as they can have a significant negative impact on the health of the whole herd due to the potential for cow-to-cow spread.

In a case of clinical mastitis, a cell count of 300,00 - 400,000 cells/mL would be detected indicating an active infection, with the cow probably showing clear signs and symptoms of illness that have already triggered further investigation and management.

Why investigate high SCC cows?

A high SCC is a sign of infection or inflammation in the udder, but it also leads to lower milk production, leading to a direct financial impact for the farm. In addition, SCC levels are associated with milk quality (protein and fat content).

Milk processors use bulk-tank SCC levels as an indicator of the milk quality. Many will offer either receive a bonus for low bulk-milk SCC levels, or penalties for high bulk-milk SCC levels. This multiplies the financial benefit for the farmer of reducing herd SCC count.

Reducing herd SCC counts can be approached through a mix of herd-level actions (such as minimising or eliminating potential environmental causes of mastitis, and minimising opportunities for cow-to-cow infection spread), and treating or managing the individual cows where an elevated individual SCC count is indicating an underlying untreated infection. (4)

Investigating high SCC cows with culture testing - a practical approach

After a herd test, some vets recommend taking the highest 10 or 20 results from each herd test, and investigating them further through culture testing. This systematic approach can be more practical for farms than trying to investigate every cow above a set cut-off.

Culture testing allows you to identify the causative bacteria in chronic infections cases, and to put in place management plans and appropriate mastitis control plans.

Mastatest has a specific HiSCC cartridge available, which focusses on identifying the most important bacterial types for chronic infections such as Staph. aureus. Each cartridge allow testing of two samples at once, and results are returned within 24hrs to both the farm and their vet. To find out more about Mastatest for HiSCC testing contact us.

1. Schukken, Y. H., González, R. N., Tikofsky, L. L., & Schulte, H. F. (2003). Monitoring udder health and milk quality using somatic cell counts. Proceedings of the National Mastitis Council, pp. 15-24.

2. Ruegg, P. L. (2017). A 100-year review: Mastitis detection, management, and prevention. Journal of Dairy Science, 100(12), 10381-10397.

3. DairyNZ guidance (Available at: https://www.dairynz.co.nz/media/jsdlrogp/smartsamm_technote_12_use_individual_cow_scc_for_management_decisions_2012.pdf )

4. AHDB guidance (Available at: https://ahdb.org.uk/somatic-cell-count-milk-quality-indicator#:~:text=The%20SCC%20is%20quantified%20as,cells%20per%20ml%20of%20milk.&text=An%20individual%20cow%20SCC%20of,cow%20is%20infected%20with%20mastitis.)