Mastitis / High Somatic Cells

What is it?

Mastitis, an udder inflammation caused by bacterial infections, leads to high somatic cell counts (SCC) in milk. Subclinical mastitis, often without visible signs, decreases milk production, lowers milk quality, and impacts fertility and overall health. Teat canals need high calcium to contract the muscles and seal the canal effectively. Excess magnesium in early lactation reduces seal tightness after milking, allowing bacteria to enter the canal.

Symptoms

Decreased milk production
Hot, swollen, painful udders
Flecks or clots in milk
Reduced milk quality
Milk tests show persistently high SCC

At a glance

Mastitis is udder inflammation caused mainly by bacterial infection and is the key driver of high somatic cell counts (SCC) in milk. Subclinical mastitis is often invisible but still reduces yield, milk quality and fertility. Teat canal closure after milking relies on calcium-driven muscle contraction. Excess magnesium and other mineral imbalances in early lactation can reduce teat seal effectiveness and make it easier for bacteria to enter.

Focus on

Udder hygiene
Minimising teat damage
Consistent nutrition
Check mineral balance to reduce mastitis pressure in the critical dry-to-early-lactation window.

Need more help? Talk to your Agvance Consultant today

What you might notice on-farm

Watch for both clinical and subclinical signs:

Decreased milk yield in individual cows or the herd
Hot, swollen or painful udders and cows that kick or resist milking
Flecks, clots or discoloured milk from one or more quarters
Elevated bulk milk SCC or repeated high individual cow SCC results
More cows requiring treatment around calving or rising mastitis cases in early lactation

Subclinical mastitis will not show obvious udder changes but will show up as persistently high SCC, reduced yield and poorer reproductive performance. If you see a pattern, act early rather than treating each case in isolation.

What good looks like

Low herd bulk SCC consistent with your seasonal benchmark and processor limits
Few clinical mastitis cases per 100 cows in early lactation and rapid recovery when treatments are applied Clear dry-off hygiene, effective teat sealing, and minimal teat damage or rough handling in the yards
A close-up and early-lactation nutrition plan that supports immune function and maintains calcium and magnesium balance

Follow these quick checklists

What to do today

Walk the herd and identify cows with abnormal milk or swollen quarters, flag them for immediate inspection.
Check milking routine and stock handling for anything rough that could damage teats.
Review recent bulk SCC trends and individual cow records for recurring high SCC cows.
Check teat condition after milking and note any rough or hyperkeratotic teats.

What to do this week

Randomly sample fresh calved cows or those flagged by milk recording for SCC and culture where possible to identify common pathogens.
Review dry-off protocol and teat preparation. Are teat sealants and drying-off hygiene being applied consistently?
Check yard surfaces and stand-off areas for contamination points such as dirty lanes, broken troughs or effluent build-up.
Reassess milking machine function with your technician if you suspect incomplete milking, liner slip or vacuum problems.

During early lactation

Prioritise prompt treatment of clinical cases and follow up with re-checks and milk recording results.
Isolate repeat offenders or chronic high SCC cows and consider culling or targeted treatment decisions with your vet.
Maintain calm handling, reduce stress on fresh cows and ensure consistent feed and water access to support immune resilience.

Issues, likely causes and where to start

If mastitis or SCC is rising, treat it like a system issue. Common causes and first checks are below.

If many fresh cows have clinical mastitis

Likely causes:

Poor dry-off hygiene or incomplete udder involution leading to infections carried through calving
Teat damage from rough handling, poor yard surfaces or poor liner fit on the machine
High pathogen load in stand-off, feed pad or calving areas

Start with:

Review dry-off practices and check consistency of teat preparation and sealant use.
Walk the calving and fresh cow areas for contamination sources and fix yard or feed pad hygiene issues.
Check milking routines and milking machine performance, including liners and vacuum levels.

For more information, read Mastitis prevention during dry off

If bulk SCC or subclinical mastitis is rising without many clinical cases

Likely causes:

Ongoing low level infections in the herd that were not cleared at dry-off
Environmental pathogens building in housing or run-off areas during wet weather
Mineral or nutritional gaps impairing immune response

Start with:

Use culture or PCR testing on a representative sample to identify pathogens and tailor treatment or control plans.
Revisit dry cow antibiotic and sealant strategy with your vet.
Review nutrition and mineral status, especially calcium, magnesium, selenium and the trace minerals that support immune function.

If teat ends are rough or cows show incomplete teat seal

Likely causes:

Overmilking, poor machine fit or inappropriate liner condition causing teat end damage
Mineral imbalances such as low calcium at milking or excess magnesium that reduce teat sphincter contractility
High milking frequency or rough handling

Start with:

Check milking machine settings and have your technician inspect liners and vacuum.
Monitor teat condition and alter milking routines to minimise overmilking.
Review mineral plan and discuss with your adviser whether any adjustments are needed around calving.

When to call the vet

Call your vet promptly if:

You have multiple clinical mastitis cases in a short period or a clear herd-level rise in SCC
You see severe infections, systemic signs, or cows that are not improving after initial treatment
Cultures show unusual or highly contagious pathogens such as Strep agalactiae or Staph aureus that need a herd approach
You need help auditing dry-off protocols, developing a targeted control plan, or interpreting bulk milk or culture results

How minerals fit in

Minerals do not cure infections, but they play a key role in supporting udder defences and effective teat closure.

Why minerals matter for udder health:

Calcium is central to muscle contraction including the teat sphincter. Adequate calcium around milking helps the teat canal close and reduces the window for bacterial entry.
Magnesium influences neuromuscular function. Excess magnesium in early lactation can reduce seal tightness after milking and increase infection risk.
Trace minerals such as selenium, copper and zinc are linked to immune cell function and wound healing, influencing mastitis resistance and recovery.

Practical mineral checks

Match mineral delivery to your system so all cows get a useful daily intake. Free-choice minerals can work but monitor who is eating them. In-shed or in-feed delivery is more controlled.
Check whether close-up and fresh cow rations are diluting or altering mineral intake. Crops and supplements can change mineral balance quickly.
Work with your adviser or vet to test for deficiencies if you suspect mineral-driven immunity or teat tone issues.

To learn more about where minerals fit in, read The Big Three Macrominerals in late lactation

FAQs

What are the first steps when I spot a cow with clinical mastitis?

Isolate the cow if practical, examine the affected quarter, take a milk sample for culture if possible, start prompt treatment following your vet’s protocol and record the case. Check milking routine to avoid spreading infection.

How does dry-off affect mastitis risk?

The dry period is when infections can be cured or established. Poor dry-off hygiene, short dry periods, incomplete drying off or inconsistent use of sealants increase mastitis risk after calving.

Can poor minerals alone cause mastitis?

No, minerals alone do not cause infection. But mineral imbalances can reduce teat seal effectiveness and immune response, increasing a cow’s susceptibility to mastitis when exposed to pathogens.

Should I cull cows with repeated high SCC?

Chronic high SCC cows are often less responsive to treatment. Discuss with your vet whether targeted treatments, segregation or culling are the most cost-effective options for your herd.

How often should I test herds for subclinical mastitis?

Frequency depends on your risk and goals. Consider testing fresh calved cows when you suspect increased pressure, and use routine recording and periodic sampling to monitor trends and the effectiveness of control measures.