What Is Mastitis in Cows and What Are the Signs?
Mastitis is inflammation of the mammary gland, or udder, and is one of the most important health problems to recognize in dairy and nursing cows.
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By Michel Scavuzzo, Founder, PetCompanionAI
Accountable authorship and editorial standards are explained in the Trust Center.
Quick answer
Mastitis may begin in one part of the udder, but severe disease can affect the entire animal.
This is educational context, not a diagnosis. Read the full explanation and sources below.
It is commonly associated with bacterial infection, although inflammation can have other causes.
Some cases produce obvious changes in the udder and milk. Others are much harder to see.
Knowing what your cow normally looks and acts like can help you recognize a problem early.
What Causes Mastitis?
Bacteria can enter the udder through the teat canal and multiply within the mammary gland.
Exposure can occur through contaminated bedding, manure, mud, milking equipment, hands, environmental conditions, or other sources.
Damage to the teats and problems with milking procedures can also increase risk.
Different organisms can cause mastitis, which is one reason treatment shouldn’t simply be guessed based on appearance alone.
What Are the Signs of Mastitis?
Depending on the severity and cause, you may notice:
- Swelling of the udder
- Heat in one or more quarters
- Redness
- Pain or sensitivity when the udder is touched
- Hardness or firmness
- Changes in the milk
- Clots, flakes, or stringy material in milk
- Watery or otherwise abnormal-looking milk
- Reduced milk production
- Loss of appetite
- Fever
- Lethargy or weakness
- Dehydration
- A cow separating herself from the herd
A cow doesn’t need to have every symptom to have mastitis.
Check Each Quarter of the Udder
A cow’s udder is divided into four separate quarters.
Mastitis may affect only one quarter rather than the entire udder.
This means comparing one quarter with another can be useful.
Does one feel hotter?
Does one look larger?
Is one unusually firm?
Does the cow react when you touch a particular quarter?
Is the milk from one quarter different from the others?
Knowing what your cow’s normal udder feels like makes abnormalities much easier to recognize.
The Milk May Tell You Something Is Wrong
Visible changes in milk can be one of the easiest signs to notice.
Milk affected by clinical mastitis may contain flakes, clots, strings, or other abnormal material. It may appear watery or otherwise different from the cow’s normal milk.
Milk production may also suddenly decline.
If you milk your cows regularly, pay attention to changes rather than looking only at the amount produced.
What Is Subclinical Mastitis?
Not every case is visible.
Subclinical mastitis means inflammation is present without the obvious udder or milk changes associated with clinical mastitis.
The cow may appear normal while measures such as the milk’s somatic cell count indicate inflammation.
This is particularly important in dairy herds because subclinical infections can affect milk production and herd health without producing dramatic outward symptoms.
Milk-testing programs and tests such as the California Mastitis Test can help identify cows or individual quarters that may need further evaluation.
Can Mastitis Make a Cow Seriously Sick?
Yes.
Some cases remain localized primarily to the udder.
Severe mastitis can affect the entire animal.
A seriously affected cow may develop fever or an abnormally low temperature, stop eating, become dehydrated or weak, lie down excessively, or appear severely ill.
In the most serious cases, toxins and systemic illness can become life-threatening.
A cow showing significant whole-body illness along with suspected mastitis needs prompt veterinary attention.
What Should You Do If You Suspect Mastitis?
Contact your veterinarian, particularly when the cow is visibly ill, symptoms are severe, or you are uncertain about the cause.
Treatment depends on factors such as the organism involved, severity of the disease, the affected cow, and whether medications are appropriate.
Don’t assume every case needs the same treatment.
Veterinary testing, including milk culture in some situations, can help determine what organism is involved and guide treatment decisions.
Be Careful With Milk From a Treated Cow
If medications are used, follow all required milk and meat withdrawal times exactly.
Milk from a cow receiving certain medications cannot legally or safely enter the human food supply until the specified withdrawal period has passed.
Treatment records are important.
Know what was given, how much was administered, when it was administered, and when the withdrawal period ends.
Can Mastitis Be Prevented?
Not every case can be prevented, but good management can reduce risk.
Important practices can include:
- Keeping bedding clean and dry
- Maintaining clean milking equipment
- Using appropriate milking hygiene
- Keeping teats clean
- Avoiding unnecessary teat injuries
- Maintaining milking equipment correctly
- Following appropriate pre- and post-milking procedures
- Monitoring cows for early udder and milk changes
- Managing flies and environmental contamination
- Keeping accurate health records
The exact prevention program will depend on whether you’re managing a commercial dairy herd, family milk cow, beef cattle, or nursing cow with a calf.
Don’t Forget Nursing Beef Cows
Mastitis isn’t limited to dairy cattle.
Beef cows nursing calves can develop it too.
Because you aren’t examining their milk at every milking, the problem can sometimes be less obvious.
Watch the udder and the calf.
A calf repeatedly attempting to nurse without appearing satisfied, avoiding one quarter, or failing to grow appropriately may give you a reason to examine the cow more closely.
Make the Udder Part of Your Routine
You don’t have to wait until a cow looks seriously ill before paying attention to her udder.
Know what is normal.
Look for changes in size and symmetry.
Feel for unusual heat, swelling, firmness, or tenderness when it is safe to do so.
Watch the milk.
Watch production.
And most importantly, watch the cow.
Mastitis may begin in one part of the udder, but severe disease can affect the entire animal.
The earlier you recognize that something has changed, the sooner you can determine what your cow needs.