Somatic Cell Count: What’s Normal?

Somatic cell count, or SCC, is the standard yardstick for udder health in milk. A normal number is lower than most people expect, and the limit that matters most is the one set by your buyer and by regulation.

Key points

SCC measures white blood cells in milk and is a standard marker of udder health.
Your milk buyer and state rules set the legal and premium limits, so confirm them directly.
Check both the bulk tank and individual cows to find the source of a problem.
Know whether contagious or environmental bacteria are driving infections.
Follow withdrawal times exactly for any treated cow.

What somatic cells are

Somatic cells are mostly white blood cells that move into the udder to fight infection, along with a small share of worn-out cells from the udder lining. Every cow has some in her milk. A healthy quarter has a low count because there is little for the body to fight.

When bacteria enter the udder, the body sends in many more white blood cells, and the count rises. That is why SCC is used as a measure of mastitis in the herd, even when no one sees clots or a swollen quarter.

What counts as normal

A healthy, uninfected quarter produces milk with a low count, and a herd of mostly healthy cows will have a low bulk tank number. Regulations and milk buyers set upper limits for what can be shipped, and many buyers pay premiums for milk well below those limits. The exact numbers depend on your market and change over time, so get them from your milk buyer or your state department of agriculture rather than from a website.

For your own herd, ask your veterinarian or extension specialist what a good target is for your size and system. Treat the buyer's limit as a ceiling, not a goal.

Do not compare your herd to a neighbor's without knowing their housing, size and sampling method. A fair comparison uses the same measure, taken the same way, from a herd with a similar setup.

Bulk tank versus individual cows

The bulk tank number is an average of every cow in the tank, so one or two high cows can pull it up noticeably. Individual cow counts, from DHIA or a milk meter system, show you which animals are responsible. Looking at both is the only way to find the source of a problem.

A few things to remember when you compare the two.

Fresh cows often run higher for a short time after calving
Late lactation cows tend to have higher counts naturally
Older cows are more likely to carry chronic infections
Cows with a single high test may be recovering, while repeated high tests suggest a chronic infection

What pushes counts up

Contagious bacteria spread from cow to cow, usually during milking. Environmental bacteria come from bedding, manure and mud, and they infect the udder between milkings. Stress, heat, poor teat condition, worn liners and inconsistent routines make either type more likely.

Because the causes differ, culture results matter. Your vet or a milk quality lab can help identify which bacteria are present so you can aim your prevention at the right route of infection.

How to track counts

Keep a simple list of cows with high tests, their lactation stage, quarters affected, culture results if you have them, and what was decided. Review it with your vet at herd health visits. Mark each cow as monitor, treat under vet direction, segregate, or cull.

Remember that any treated cow has a withdrawal period for milk and meat. Follow the label or your vet's instructions exactly and keep her milk out of the tank until the time is up.

If you use a cow-side or in-parlor test, ask your vet how to interpret it, since those tests are screening tools rather than a full diagnosis.

Common mistakes

Many herds wait for the buyer's warning letter before looking at SCC. By then the problem has usually run for weeks. Others focus only on dry cow or lactation treatment and overlook teat dipping, liner changes and bedding.

Another trap is milking known high cows into the tank because the count seems fine this week. Averages can look acceptable while the infection keeps spreading.

Ignoring individual cow counts
Skipping culture and relying on guesses
Letting teat dip or prep routines slip
Keeping chronically infected cows in the milking string without a plan

What to ask your vet or milk quality specialist

Bring your last several tests and a list of high cows to your next visit. Ask which bacteria are most likely in your herd, whether contagious or environmental causes dominate, and which parts of the milking routine to observe first.

Ask also whether a milking time evaluation or an equipment test is due. Often the fastest route to lower counts is a careful look at how cows are prepared, milked and dipped.

When to get help: Call your veterinarian when counts rise for more than a short stretch, or when cows show clots, swelling or sudden drops in milk. Ask your milk buyer or state department of agriculture for the current limits that apply to you.

Sources and further reading

Organization homepages are linked so you can search them for current guidance on this topic.

More in Milk Quality, Business & Sustainability

← Milk Quality Benchmarks Every Dairy Should Know Reducing Bulk Tank SCC →