Mastitis in cows: somatic cell counts (SCCs)

Find out how monitoring somatic cell counts (SCCs) can help us to identify mastitis. 

What are somatic cells?

Somatic cells are mainly the living and dead white blood cells and some dead udder cells, which end up in the milk.

What are somatic cell counts?

There are always small numbers of immune cells in a cow’s milk, which protect the udder against infection by bacteria. When cows get mastitis, their somatic cell counts (SCCs) increase dramatically as white blood cells flood into the quarter to tackle the infection. The clots found in the milk of cows with mastitis are mainly clumps of dead white blood cells.

Once infection has been cleared, the SCC gradually drops to a normal level. This can sometimes take weeks.

In cases of subclinical and chronic infection, in which the bacteria persist in the udder, SCCs can remain high throughout lactation, or may fluctuate. SCCs also tend to be higher in older cows, immediately after calving and towards the end of each lactation period.

How can SCCs be used to identify infection?

Individual cow SCCs are used to identify cows that are likely to have an intramammary infection. The California Milk Test can be used to detect the increased SCC of milk from quarters with subclinical mastitis (see Control of contagious mastitis factsheet for further details).

SCCs are used as a measure of:

• The likelihood of a cow being infected with mastitis bacteria: if a cow’s SCC is more than 200,000 cells/ml, she is more likely to be infected
• The quality of the milk produced

Mastitis can affect the composition of milk, its keeping abilities, its taste and how well it can be made into other dairy products, such as yoghurt or cheese.

Milk contracts often define several SCC ‘thresholds’ and any respective bonus for attaining them. In the European Union, milk is not considered fit for human consumption if it has a SCC of more than 400,000 cells/ml.

Monitoring SCCs

Essentially, a lower SCC indicates better udder health. SCC monitoring is important because as the number of somatic cells increases, milk yield is likely to fall. This is primarily associated with damage to milk-producing tissue in the udder caused by mastitis pathogens and the toxins they produce, particularly when milk-producing cells are lost.