Mastitis is inflammation of the udder, almost always caused by bacterial infection entering through the teat canal. It is the single most expensive disease in dairy — typically $200–500 per clinical case once you tally lost milk, treatment, milk discard during withdrawal, and the increased risk of culling. Most cases are catchable in the first 24 hours if you know what to look for.
Quick answer Check the milk first (a strip cup or CMT before milking), then the quarter (heat, swelling, asymmetry), then the cow herself (off feed, fever, dull rumen fill). Clinical mastitis shows abnormal milk — flakes, clots, watery or bloody secretions. Subclinical mastitis shows no visible milk change but a somatic cell count above 200,000 cells/mL. Both need attention; the subclinical case is the iceberg under the surface, costing yield invisibly.
Why catching it early matters A cow with clinical mastitis treated within 24 hours of onset has a 70–85% cure rate. The same case caught at 72 hours drops to 40–60%. Chronic infections that go untreated for more than four weeks often only resolve with culling. At the herd level, a bulk-tank somatic cell count above 400,000 cells/mL costs roughly 5% of the milk price in most markets, plus penalty deductions in regions with stricter limits. Subclinical cases — invisible to the eye but every bit as costly — typically make up 70–80% of all mastitis on a working farm.
The three-quarter check at every milking Every milking is your screening opportunity. Trained staff catch mastitis in seconds with this routine, repeated on every cow.
Step 1: strip the foremilk Before attaching the cluster, hand-strip 3–4 squirts from each quarter into a dark-bottomed strip cup (or the parlor floor where regulations allow). Look for clots, flakes, blood, thin watery milk, or off colour. Normal foremilk is uniformly white, slightly viscous, and free of debris. Stripping also clears the teat canal of bacteria-laden first-draw milk before the cluster goes on — so it's both a diagnostic and a preventive step.
Step 2: palpate each quarter Run your hands over all four quarters before and after milking. Compare left to right and front to back: asymmetry is a red flag. Heat in one quarter relative to the others, hardness that doesn't soften after milking, painful response when palpated — any of these is a clinical case until proven otherwise. A healthy udder is uniformly soft, cool, and pliable after milking.
Step 3: assess the whole cow Mild mastitis affects only the udder. Moderate mastitis adds visible swelling and pain. Severe mastitis adds systemic illness: fever above 39.5 °C, depressed appetite, reduced rumen fill, dull eyes, dehydration. A cow with severe mastitis is a vet call, not a tube-and-go case.
Severity grades (NMC standard) The National Mastitis Council classifies clinical mastitis into three grades — these guide treatment urgency. Train staff to call them out by grade so the right response triggers automatically.
Grade 1 (mild) Abnormal milk only. The cow looks fine, the quarter feels fine, but the milk shows flakes or clots. Treat with intramammary antibiotic per herd protocol; most respond in 2–4 days.
Grade 2 (moderate) Abnormal milk plus an abnormal quarter (hot, swollen, painful). The cow herself is still bright and eating. Intramammary antibiotic plus an anti-inflammatory; check twice daily for 3 days.
Grade 3 (severe) Abnormal milk, abnormal quarter, plus systemic signs (fever, off feed, depression, dehydration). This is an emergency. Systemic antibiotics, IV fluids, anti-inflammatories, and often hospitalisation in a sick pen. Coliform mastitis in a fresh cow can kill within 12–24 hours if untreated — do not delay the vet call.
The subclinical iceberg For every visible clinical case there are typically 15–40 cows in the herd with subclinical mastitis. These cows produce normal-looking milk but elevated SCC. They are the dominant cost of mastitis on most farms because they suppress yield (a quarter with SCC over 500,000 produces 10–15% less than a healthy one), spread infection to herd mates at milking, push up bulk SCC and the penalty cost on every shipment, and routinely become the clinical cases of next month.
Detecting subclinical cases Three tools, used together:
California Mastitis Test (CMT) — A cow-side test. Mix equal parts foremilk and reagent in a four-well paddle, swirl, read. Trace, 1+, 2+, 3+ reactions correspond to rising SCC bands. Takes 30 seconds, costs cents per test. The standard tool for stripping out trouble cows when bulk SCC creeps up.
Individual cow SCC — Monthly DHI test or in-parlor sensors. Cows above 200,000 are flagged for follow-up; cows above 1,000,000 are chronic and usually need a treatment-or-cull decision.
Culture before treatment — If you're going to treat subclinical cases, culture first. Different pathogens respond to different drugs, and roughly 30% of clinical cases have a negative culture (immune system already won; treatment won't change the outcome). Culture-driven treatment cuts antibiotic use by 30–50% on most farms with no loss of cure rate.
Contagious vs environmental pathogens Knowing the source of infection changes the response.
Contagious pathogens spread cow-to-cow at milking. The big three: Staphylococcus aureus (chronic, hard to cure, hides inside cells where antibiotics struggle to reach), Streptococcus agalactiae (cures readily with penicillin if you catch it early), and Mycoplasma bovis (incurable — cull). Spread is via contaminated hands, teat-cup liners, and towels. Prevention: post-milking teat dip on every cow every milking, single-use towels, glove changes between cows or batches, and segregating known infected cows to the end of the milking order.
Environmental pathogens live in bedding, manure, water, and soil. Coliforms (E. coli, Klebsiella) cause acute severe cases — often the Grade 3 emergencies in fresh cows. Streptococcus uberis is the most common environmental pathogen worldwide. Prevention: clean dry bedding refreshed frequently, internal teat sealants at dry-off, well-functioning ventilation, and no standing water in alleys or collection yards.
Mistakes that cost money
Treating without culture in a herd with persistently high subclinical SCC. You burn antibiotic on infections that wouldn't respond to that drug anyway and keep withholding milk for no benefit.
Skipping pre-milking strip-cup checks because "it slows things down." Catching a clinical case at 12 hours instead of 48 hours doubles cure rate — there is no faster return on labour in the parlor.
Treating only the clinical quarter and moving on. The other three quarters in the same cow are at high risk too, but more importantly the pathogens she carried have likely already spread to herd mates. Investigate herd-wide.
Returning a treated cow to the milking string before her withdrawal period ends. Withdrawal periods are not suggestions; milk-residue test failures cost the entire bulk tank.
Ignoring chronic high-SCC cows. A cow above 500,000 for three consecutive monthly tests will not "snap out of it" on her own. She is both a reservoir for the herd and a permanent drag on yield.
When to call the vet
Any Grade 3 case (systemic signs). Coliform mastitis in a fresh cow needs aggressive supportive care — do not wait until morning.
Multiple clinical cases within the same week. Herd outbreaks suggest a milking-equipment problem, a contagious pathogen on the verge of spreading, or a housing or hygiene breakdown.
Repeat cases in the same cow within 30 days. Either the original treatment failed (wrong drug, chronic Staph aureus) or the cow has structural teat-end damage that keeps inviting infection.
Visible blood in the milk of a non-fresh cow. Mastitis bleeds occasionally, but blood plus systemic signs can indicate severe E. coli or a teat-end injury. Get diagnostics quickly.
Bulk-tank SCC trending up over consecutive shipments with no obvious clinical cause. That is a subclinical epidemic — get a herd workup, cull the chronics, and audit the milking routine.
Tracking it in Vache When you spot signs of mastitis, log a health event on the cow's profile with type "mastitis" and free-text notes for the affected quarter, milk appearance, and treatment given. Set a withdrawal end date so the cow appears in the withdrawal-hold filter on the milk-recording screen — you will not accidentally ship her milk.
If you are doing in-parlor CMTs or sending samples for individual SCC, use the Quality tab on the cow profile to record sample dates, SCC values, and fat/protein/lactose percentages. Over time the SCC trend chart on each cow's page will make chronic cases visually obvious — a flat line under 200,000 versus a sawtooth above 400,000 tells the story before you look at any other record.
At the herd level, the dashboard's data-quality panel surfaces cows with no milk-quality samples and cows with no health history. Both are reasonable proxies for "we have not been watching closely enough." Filling those gaps is the cheapest mastitis intervention available.
Frequently asked questions
Should I keep milking a cow with clinical mastitis? Yes — strip the affected quarter out fully at every milking, but discard that milk (do not let it go in the tank). Frequent stripping physically removes bacteria and inflammatory products and is part of the cure. Keep her in the milking string but milk her last to prevent spread.
How fast should I see improvement after treatment? Most cases improve within 24–48 hours: the milk clears, swelling reduces, the cow's demeanor improves. If you do not see improvement at 48 hours, the treatment is failing — culture and reassess. Either the pathogen is resistant to the chosen drug, the drug is wrong, or you are dealing with a chronic infection that won't respond.
Can mastitis spread to humans? Modern pasteurization kills mastitis pathogens. Direct contact (handling an infected cow without gloves) can occasionally cause minor skin infections, and historically Strep agalactiae was a serious raw-milk pathogen. The public-health risk in pasteurised markets is negligible — but wear gloves anyway, and never drink milk from a treated cow.
Will the affected quarter come back? Depends on the pathogen, the duration of the infection, and the cow's age. Strep agalactiae quarters typically recover fully. Staph aureus quarters often become chronic — they may produce milk again but at reduced volume with permanently elevated SCC. Severe E. coli toxic mastitis can permanently destroy mammary tissue (a "blind quarter"); the cow can still be productive on three quarters.
How do I know a cow is actually cured after treatment? Two consecutive negative bacterial cultures, taken 14 and 21 days after the last treatment, with SCC dropping back to normal levels. Visual milk appearance alone is not enough — many cows look normal but are still shedding bacteria into the bulk tank.
What's the difference between mastitis and milk fever? Different diseases, frequently confused by new farm staff. Mastitis is an udder infection. Milk fever (hypocalcemia) is a calcium-deficiency metabolic disease that strikes in the first 48 hours after calving, presents with a wobbly cow that goes down and may have a cold udder, and is treated with IV calcium. A fresh cow that's down on her feet needs differential diagnosis — the two can occur together but treatments are completely different.
Sources National Mastitis Council (NMC) — Recommended Mastitis Control Program. AHDB Dairy — Mastitis Control Plan. Royal Veterinary College (UK) — Bovine Mastitis Pathogens factsheet. Penn State Extension — Mastitis Diagnosis and Treatment. The Merck Veterinary Manual — Mastitis in Cattle.