Mastitis in cows is the most common health problem in dairy cattle and the one that costs family cow owners the most milk, usually without them realizing it is happening. The dramatic version, a hot swollen quarter and clotted milk, is the version everyone knows. The expensive version is the one you cannot see. This is how to catch it early, what to do when you find it, and the handful of practices that prevent most of it.
If you are new to milking generally, our guide to milking a cow covers the daily routine and hygiene steps that this article builds on.
Key Takeaways
What Is Mastitis in Cows?
Mastitis is inflammation of the mammary gland, almost always caused by bacteria entering through the teat canal. It comes in two forms, and the difference matters enormously for how you find it.
Clinical mastitis is the visible kind. The milk goes abnormal, showing flakes, clots, strings, or a watery discoloration. The quarter may be hot, hard, swollen, or painful. In severe cases the cow herself becomes systemically ill: off feed, dull, feverish, sometimes down. You will not miss this one if you are checking milk before each session.
Subclinical mastitis is the one that matters more, because it produces no visible symptoms at all. The udder looks fine, the milk looks fine, and yield and quality drop anyway. It is far more common than the clinical form, it goes undetected for months in herds that are not testing, and it is the reason a cow who seems healthy is producing less than she should.
The standard measure is somatic cell count. According to University of Minnesota Extension’s guidance on solving mastitis problems, an SCC above 200,000 cells per milliliter indicates infection, and a cow sitting above that threshold for two or more months is considered chronically infected.
How to Detect Mastitis Early
Three tools, in ascending order of effort, and a homestead should use the first two routinely.
The strip cup, before every single milking. Strip the first few squirts from each quarter into a dark-bottomed cup or onto a dark plate and look at them. This takes fifteen seconds, it catches clinical cases before you contaminate a whole bucket, and it is the single highest-value habit in a milking routine. Never strip onto the ground or your hand, because you cannot see anything and you spread organizms.
The California Mastitis Test. This is the practical way for a homesteader to find subclinical infection. You mix a sample from each quarter with a reagent on a paddle and watch how it gels. More gelling means more somatic cells means more inflammation. The test is inexpensive, keeps well, works quarter by quarter so you know which one is affected, and requires no lab. Run it monthly on a family cow, and immediately on any cow whose production drops without explanation.
Laboratory culture and SCC testing. For a persistent or recurring problem, culturing a sample tells you which organizm you are actually dealing with, which determines whether your problem is a hygiene problem or a milking-procedure problem. UMN Extension’s recommendation for herds working through a mastitis problem is to culture the most recent 10 to 30 clinical cases rather than treating each one blind.
The Two Kinds of Mastitis Organizms
This distinction is the single most useful thing to understand, because it tells you where the infection is coming from and therefore what to change.
Contagious organizms include *Streptococcus agalactiae*, *Staphylococcus aureus*, and *Mycoplasma*. These live inside the udder, are well adapted to surviving there, and spread from cow to cow during the milking process itself, carried on hands, cloths, and milking equipment. If you have contagious mastitis, your problem is your milking procedure and your order of milking.
Environmental organizms include coliforms, environmental streptococci, and various staph species. These live in the cow’s environment, in bedding, mud, and manure, and the risk is directly proportional to the number of organizms sitting on the teat end when the unit or your hands go on. If you have environmental mastitis, your problem is bedding, housing, and teat preparation.
A single cow homestead almost always has an environmental problem rather than a contagious one, simply because there is no other cow to spread from. That is genuinely good news, because environmental mastitis responds to cleanliness you control directly.
Treating Mastitis
The honest answer here is that treatment is a veterinary decision and this is not a place to improvise.
Call your vet for any clinical case. Intramammary antibiotic tubes are the standard treatment for most clinical mastitis, but the choice of product depends on the organizm, and the milk withholding period depends on the product. Using the wrong tube wastes money and time while the infection establishes; ignoring a withholding period puts antibiotic residue in milk you or your family will drink.
What you can do without waiting: strip the affected quarter out frequently and completely, since removing infected milk is genuinely therapeutic. Keep the cow comfortable, hydrated, and eating. Milk the affected quarter last, into a separate container, and dispose of that milk rather than feeding it to other animals.
Two things not to do. Do not stop milking an infected quarter to “rest” it, since that traps infected material inside. And do not assume a quarter that looks better after two days is cured, because clearing visible symptoms is not the same as clearing the infection.
Some cases do not resolve. A chronically infected quarter that fails repeated treatment is sometimes best dried off permanently, and a cow with recurring mastitis across multiple lactations is a real culling conversation. That is a hard call on a family cow with a name, but a chronically infected animal is both a welfare issue and a reservoir of infection.
Preventing Mastitis
Prevention is where nearly all the return is, and the practices with the most evidence behind them are practices a one-cow operation can absolutely do.
Post-milking teat dip, every teat, every time. UMN Extension lists complete post-milking teat dip coverage as a core practice against both contagious and environmental organizms. The teat canal stays open for a period after milking, and the dip protects it during exactly that window. This is the highest-return thirty seconds in the entire routine.
Clean, dry teats before the unit or your hands go on. Not damp, not wiped with the same cloth you used on the last cow. Individual towels or wipes per animal, and dry thoroughly, since a wet teat carries organizms straight down.
Working milking equipment. If you use a machine, have it checked and serviced. Liner slips, the squawking sound of air getting in, drive contaminated droplets up against the teat end. Worn liners and incorrect vacuum are ordinary causes of an ongoing mastitis problem.
Milk infected cows last. If you have more than one animal and one is known positive, she goes at the end of the order every time, and ideally with separate equipment. This is the single most effective control for contagious spread.
Dry cow therapy and teat sealants. UMN Extension specifically names internal or external teat sealants at dry off. The dry period is a genuinely high-risk window for new infections, and sealing the teat canal closes the door on it. Discuss with your vet whether this fits your animal.
Clean, dry bedding. For environmental mastitis this is the whole ballgame. A cow lying in mud or soiled bedding presses a dirty teat end against the ground for hours at a time. Our guide to keeping livestock cool in the heat covers the summer side of housing, when heat, humidity, and flies all raise environmental pressure at once.
Fly control. Flies carry organizms between animals and cause teat irritation that opens the door. Our guide to keeping flies away covers the practical options.
Does Breed or Management Change the Risk?
Somewhat, though the effect is smaller than management.
Udder conformation matters. A cow with a deep, pendulous udder that hangs closer to the ground picks up more environmental contamination than a cow with a well-attached, higher udder, which is one reason udder attachment is worth looking at when you buy. Our guide to choosing cow breeds for milk, meat, or both covers the breed characteristics worth weighing, and our Jersey cow guide goes deeper on the family cow most homesteaders end up with.
Higher-producing animals carry somewhat higher risk simply because more milk moving through means more opportunity. And the transition into and out of the dry period is the highest-risk window of the whole year, which is exactly why dry cow therapy exists.
None of that changes the core answer. Clean teats, a working routine, teat dip after every milking, dry bedding, and a strip cup you actually use will prevent most of the mastitis you would otherwise get.
Frequently Asked Questions
What are the signs of mastitis in a cow?
Clinical mastitis shows abnormal milk with flakes, clots, strings, or watery discoloration, often with a hot, hard, or swollen quarter. Subclinical mastitis shows nothing at all, which is why it is more common and more costly. A somatic cell count above 200,000 cells per milliliter indicates infection even when everything looks normal.
How do you test for mastitis at home?
Use a strip cup before every milking to catch clinical cases, and a California Mastitis Test monthly to catch subclinical ones. The CMT is inexpensive, needs no lab, and tests each quarter separately so you know exactly which one is affected.
What causes mastitis in cows?
Bacteria entering the teat canal, from two distinct sources. Contagious organizms like Staph aureus and Strep agalactiae live in the udder and spread cow to cow during milking. Environmental organizms like coliforms live in bedding and manure and get in from a dirty teat end. A one-cow homestead almost always has an environmental problem.
How do you treat mastitis in a cow?
Call your vet. Intramammary antibiotic tubes are standard, but the right product depends on the organizm and each has its own milk withholding period. Meanwhile, strip the affected quarter out frequently and completely, milk it last into a separate container, and discard that milk. Never stop milking an infected quarter to rest it.
Can you drink milk from a cow with mastitis?
No. Discard milk from an affected quarter, and observe the full withholding period for any antibiotic used. Milk from a treated cow is not safe to drink or to feed to other animals until that period has passed.
