Nov 7, 2026·DairyLogs Team
Mastitis in cows is the costliest dairy disease. Learn the symptoms, causes, CMT and SCC tests, treatment options and a 10-step plan to prevent it on your farm.
Mastitis in cows is the most common and most expensive disease on dairy farms worldwide. It quietly cuts milk yield, raises somatic cell counts, forces you to dump milk and sends good cows to the cull pen early.
A single clinical case in early lactation has been estimated to cost about US$444 once lost milk, drugs, discarded milk, labour and culling risk are added up (Rollin et al., 2015).
The good news: most mastitis is preventable. This guide explains what mastitis in cows is, how to spot it early, what causes it, how it is treated, and the step-by-step prevention plan that keeps herds healthy.
Photo: Muhammad Mahdi Karim, GFDL 1.2, via Wikimedia Commons
Quick answer: Mastitis in cows is inflammation of the udder, almost always caused by bacteria entering through the teat canal. Signs include clots or watery milk, a swollen, hot or painful quarter and, in severe cases, fever and loss of appetite. Treat early with your vet's guidance, and prevent it with clean, dry bedding, good milking hygiene, post-milking teat dipping, dry cow management and culling of chronic cases.
Log every mastitis case and treatment free → Start free
Mastitis is inflammation of the mammary gland (udder). In dairy cows it is nearly always the cow's immune response to bacteria that have entered a quarter through the teat end. The body sends white blood cells (somatic cells) into the milk to fight the infection. That is why a rising somatic cell count (SCC) is the classic sign of mastitis, even when the milk looks normal.
Each of the four quarters is a separate gland, so one quarter can be infected while the others stay healthy.
You can see it. The milk, the udder or the cow look abnormal. Vets usually grade clinical cases by severity:
Mild (grade 1): abnormal milk only, such as flakes, clots or watery milk. The udder and cow look normal.
Moderate (grade 2): abnormal milk plus a swollen, hard, hot or painful quarter.
Severe (grade 3): the cow herself is sick, with fever, depression, loss of appetite, dehydration or lying down. This is often caused by E. coli or other coliforms and can be fatal without fast treatment.
The milk looks normal, but the quarter is infected and SCC is high. Subclinical mastitis is far more common than clinical mastitis. For every clinical case on a farm, there are usually many more cows with hidden infections that are cutting yield and spreading bacteria at every milking.
A long-lasting infection that flares up repeatedly or never fully clears, often caused by Staphylococcus aureus. Chronic cows act as a reservoir of infection for the rest of the herd.
Photo: L. Mahin, CC BY-SA 3.0, via Wikimedia Commons
Check for these signs during every milking:
Changes in the milk: clots, flakes, strings, pus, blood, or watery, yellowish milk
Changes in the udder: a quarter that is swollen, hard, hot, red or painful to touch
Behaviour: kicking at the cluster, restlessness or uneven milk-out
Milk yield: a sudden drop in one cow's daily milk
Whole-cow signs (severe cases): fever above 39.5°C (103°F), dull eyes, off feed, rapid breathing, diarrhoea, dehydration or a cow that will not stand
A sudden drop in a cow's yield is often the first sign of mastitis, sometimes a day before the milk changes. Farms that record milk per cow catch these drops much earlier than farms that only look at the bulk tank.
Photo: Mohammad Golkar, CC BY-SA 4.0, via Wikimedia Commons
Gangrenous mastitis (above) is the most severe form. The quarter turns blue-black and cold, and the cow is in danger. Call your vet immediately.
Photo: Eric Erbe and Christopher Pooley, USDA ARS, Public domain, via Wikimedia Commons
Mastitis bacteria fall into two main groups. Knowing which group is causing problems on your farm tells you where to focus.
Factor | Contagious mastitis | Environmental mastitis |
|---|---|---|
Main bacteria | Staphylococcus aureus, Streptococcus agalactiae, Mycoplasma bovis | E. coli, Klebsiella, Streptococcus uberis |
Where they live | Inside infected udders and on teat skin | Manure, wet bedding, mud and dirty water |
How they spread | Cow to cow during milking: milkers' hands, cloths, liners | From the environment to the teat end between milkings |
Typical pattern | High herd SCC, many subclinical and chronic cows | More clinical cases, often severe, especially around calving and in wet weather |
Main control | Milking hygiene, post-dipping, dry cow therapy, culling | Clean, dry housing and bedding, pre-dipping, good transition care |
Wet, dirty bedding, muddy yards and overcrowding
Poor milking routine, unwashed hands and shared udder cloths
Faulty milking machines: wrong vacuum, worn liners, over-milking
Damaged teat ends and teat injuries
The weeks around dry-off and calving, when infection risk is highest
Milk fever and negative energy balance after calving, which weaken immunity
Low vitamin E and selenium in the diet
Heat stress and flies
Strip two or three squirts from each quarter onto a dark strip cup or plate before attaching the cluster. It is the fastest way to find clinical mastitis, and it also stimulates milk let-down.
Photo: Blonder1984, CC BY-SA 3.0, via Wikimedia Commons
The CMT is a cheap cow-side test for subclinical mastitis. Milk from each quarter goes into one of the four cups on the paddle, you add an equal amount of CMT reagent and swirl. The more the mix thickens or gels, the higher the somatic cell count:
Negative / trace: mix stays liquid; quarter is most likely healthy
Score 1: slight thickening; likely subclinical infection
Score 2: clear thickening
Score 3: gel forms and almost sticks together; strong infection
Individual cow SCC from milk recording is the best way to monitor udder health over time. As a rule of thumb, a healthy quarter has well under 100,000 cells/mL, and a cow above 200,000 cells/mL very likely has an infected quarter. Each extra 100,000 cells/mL above 200,000 is linked to roughly a 2.5% loss in milk yield.
Bulk tank SCC is regulated in many markets. The EU limit is 400,000 cells/mL and the US limit for Grade A milk is 750,000 cells/mL, but many processors pay bonuses for much lower counts.
Sending a sterile milk sample to a lab identifies the exact bacteria. This lets your vet choose the right treatment, and it tells you whether your problem is contagious or environmental. Culture is strongly recommended for recurring cases and high-SCC herds.
Free tool: Got a cow with repeat or chronic mastitis? Compare what she earns against what she costs before you decide to keep or cull her. Open the Culling Decision Calculator →
Always work with your veterinarian on a mastitis treatment plan. The right treatment depends on the bacteria, the severity and the stage of lactation. General principles:
Mild and moderate cases are often treated with intramammary antibiotic tubes into the affected quarter, as prescribed by your vet. Some mild cases caused by E. coli cure on their own, which is why many farms now culture first and treat based on the result. This can cut antibiotic use without hurting cure rates.
Severe cases are an emergency. Vets usually give anti-inflammatory drugs (NSAIDs), fluids and, where needed, systemic antibiotics. Fast treatment saves lives.
Frequent stripping of the affected quarter can help remove bacteria and toxins.
Chronic cows, especially Staph. aureus cases that relapse, rarely cure during lactation. Drying off the affected quarter or culling is often the most economic choice.
Withdrawal periods matter. Milk from treated cows must be kept out of the tank until the drug's milk withdrawal period has passed, and meat withdrawal applies too. See our guide to tracking milk withdrawal and log every treatment in DairyLogs health records so withdrawal end dates are tracked automatically.
Tip: Mark treated cows clearly (leg bands or tail tape) and milk them last or with a separate bucket unit. Antibiotic residues in the bulk tank can mean rejected milk and heavy penalties.
Photo: David Monniau, CC BY-SA 2.0 FR, via Wikimedia Commons
Prevention is far cheaper than treatment. These steps build on the National Mastitis Council's proven mastitis control principles:
Keep bedding clean and dry. Clean cubicles or sheds at least twice a day, remove wet bedding and manure, and avoid overcrowding. Teats should be clean when cows walk into the parlour.
Follow a consistent milking routine. Wear gloves, forestrip, pre-dip, wait 30 seconds, then dry each cow's teats with her own clean towel before attaching the cluster.
Post-dip every teat after every milking. Cover the whole teat barrel with an approved teat dip. This is one of the most effective steps against contagious mastitis.
Maintain the milking machine. Have vacuum level and pulsation checked regularly, replace liners on schedule, and avoid over-milking.
Keep cows standing after milking. The teat canal takes time to close. Offer fresh feed straight after milking so cows stay on their feet for 30–60 minutes.
Milk infected cows last, or use a separate unit, and disinfect the cluster afterwards.
Manage dry-off well. Use dry cow therapy and/or internal teat sealants as advised by your vet. The dry period is the best time to cure existing infections and prevent new ones. Our dry-off feeding guide explains how to prepare cows.
Feed for immunity. Provide adequate vitamin E, selenium and other trace minerals, prevent milk fever, and keep cows at the right body condition score at calving.
Treat clinical cases early and record every case so repeat offenders stand out.
Cull chronic cows. A cow with three or more clinical cases in a lactation, or a persistently high SCC, is usually costing more than she earns. Use our culling decision calculator to decide with real numbers.
Photo: Gunnar Richter, CC BY-SA 3.0, via Wikimedia Commons
Photo: Timothy Akolamazima, CC BY-SA 4.0, via Wikimedia Commons
Many small farms in Pakistan, India and Africa still milk by hand, and mastitis spreads easily from cow to cow on milkers' hands. To reduce the risk:
Wash and dry your hands before milking, and between cows if any cow has mastitis.
Use the full-hand method. Avoid "knuckling" or stripping with the thumb, which damages the teat.
Wash dirty teats with clean water and dry them with a separate cloth for each cow.
Milk healthy cows first and cows with mastitis last.
Dip teats in a teat disinfectant after milking.
Do not let calves suckle cows with mastitis.
Winter brings extra risks such as muddy yards and chapped teats. Read the winter mistakes that cut milk production to stay ahead.
Mastitis costs far more than the price of a few antibiotic tubes. The main losses are:
Lost milk from infected quarters, which often never return to full production in that lactation
Discarded milk during treatment and withdrawal
Vet visits, drugs and extra labour
Lower milk price from high bulk tank SCC
Early culling and replacement heifer costs
Deaths from severe cases
Mastitis is one of several diseases that quietly drain profit. See our full guide to dairy cow diseases, symptoms and prevention and the guide to logging health treatments.
Yes. Most mild and moderate cases recover with prompt treatment and good care. Chronic infections, especially Staph. aureus, are harder to cure, and a quarter can lose production permanently after a severe case.
Milk from cows with clinical mastitis or under antibiotic treatment should not go into the bulk tank or be used for human consumption. It can contain bacteria, toxins and drug residues. Follow the withdrawal period on the drug label and your vet's advice.
Mild clinical cases often resolve within a few days of treatment, but you must also wait out the milk withdrawal period before selling milk. Subclinical and chronic infections can last for months if not managed.
Forestripping before every milking finds clinical cases, while the California Mastitis Test and individual cow SCC find hidden (subclinical) cases.
Fresh cows in the first weeks after calving, cows in the early dry period, older high-yielding cows and cows with damaged teats or a history of mastitis.
Yes. Breeds selected for udder health, such as Norwegian Red, tend to have lower mastitis rates. Compare breeds in our guide to the highest milk yielding cow breeds.
Controlling mastitis in cows starts with good records. With DairyLogs you can log every clinical case and treatment, track withdrawal periods, spot sudden milk drops cow by cow, and see which animals keep coming back.
Better records mean faster action, fewer repeat cases and cleaner milk.
With a free DairyLogs account you can:
Log every clinical case, treatment and milk withdrawal period
Spot sudden milk drops cow by cow before mastitis spreads
See which cows keep coming back so you can plan dry cow therapy or culling
Create your free DairyLogs account → No credit card needed.
This article is for general information and does not replace advice from your veterinarian.
Want tools that match these practices? Start free with DairyLogs.
