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Bovine Mastitis

Also known as

Mammary gland infection


The term mastitis refers to inflammation of the mammary gland (udder) regardless of the cause (infection, trauma, etc.) and is characterized by changes in the milk and pathological changes in the mammary tissue.

Inflammation of the udder (mastitis) is most common in dairy cows due to the complexity and quantity of mammary tissue in these high-producing animals. It can also occur in beef cows, however, and can be serious.

Depending on the organism causing the infection, a bad case of mastitis may kill the cow if the infection does not stay localized in the udder--if it gets into the bloodstream and causes septicemia.

If infection stays localized in the udder (in the quarter that got bruised or invaded by bacteria via the teat canal) the mammary tissue in that quarter may be damaged but the infection is not life threatening. That quarter may be permanently damaged (losing its ability to produce milk), however, unless treatment is prompt and effective.  It will be small (and dry) the next time she calves, or may produce some fluid right after calving, and then dry up again.

If the infection does not stay localized, and gets into the bloodstream, the cow becomes sick. She’ll go off feed and have a fever. Unless proper treatment is begun swiftly and continued diligently, the cow may not only lose that quarter (or even part of the udder, sloughing away), but also her life.

In many cases of mastitis, milk production drops suddenly. The affected quarter is hot and swollen, tender and sore; the cow resents having it touched. If she has a calf, she may not let him nurse that quarter.

If you suspect mastitis, squirt some milk out of the affected quarter to inspect. Color or consistency may be abnormal--thin and watery or thick and full of clots. A few small abnormal flecks may be hard to detect unless you use a strip cup with a fine mesh to catch them.

Acute mastitis may respond to treatment or may subside on its own and then recur as a less painful but chronic condition, or may flare up again at a later date if the udder or the cow’s immunity is compromised again. Aftermath of mastitis may leave permanent damage and scar tissue or a lump of encapsulated pus (abscess).

Some cases of chronic mastitis are not easy to detect because the udder isn’t sore; the cow merely drops in milk production and has a few flakes or clots in the milk. In a dairy herd it’s important to always check each cow before milking, testing the first few squirts of milk with a strip cup or a mastitis screening test to check for somatic cells (body cells that may be indicative of infection).


  • Swelling
  • Redness
  • Hardness
  • Pain
  • Abnormalities in milk
  • Discoloration
  • Watery
  • Lumpy
  • Bloody
  • Drop in milk production


A wide variety of bacteria may infect the udder, including several kinds of streptococcus, several species of staphylococcus (which can be difficult to treat), and other less common pathogens. An occasional infection with Klebsiella may occur when cows are bedded on wood shavings or sawdust. This particular pathogen is a common inhabitant of tree bark.

Mastitis can develop if a quarter becomes infected by contamination from the outside environment, as when a cow lies in mud or manure and bacteria enter the teat canal. When cows calve in dirty conditions, or lie in mud/manure after calving, pathogens may enter the teat. In dairy cows, bacteria may be introduced by improper handling at milking time, or dirty milking equipment.

Mastitis may be a sequel to bruising and trauma if the udder is bumped and bruised. The damaged tissue creates ideal conditions for infection to get started even if there’s no break in the skin for pathogens to enter from outside.

If a cow has infection elsewhere in her body, and germs circulating in her bloodstream, they may find a perfect environment in bruised mammary tissue to multiply and create a serious infection.

Dairy cows’ udders are more easily bruised than beef cows’ udders, due to sheer size. A pendulous, full udder is vulnerable to bruising if the cow hurries; her udder swings back and forth if she trots or gallops and she bangs it with her hind legs.

This can also happen in a beef cow if her udder is tight and full, as at weaning time. A beef cow may still be producing a lot of milk by the time her calf is weaned, and develops a large udder when the calf is no longer nursing. It may be tight and sore for several days, and vulnerable to bruising if she is quite active.  

A tight udder (when you stop milking a dairy cow, or a beef cow’s calf is weaned) signals it to cease milk production. Eventually milk in the udder is resorbed and the cow dries up. But for several days after she’s no longer being milked/nursed, the udder is full and tight--and painful, until pressure eases off as the milk resorbs. It is very vulnerable to injury and bruising during this period.


Providing a clean environment and clean bedding is good prevention, along with making sure you don't inadvertently spread mastitis from one cow to another in a dairy herd. First-calf heifers are often most susceptible to mastitis because they may not have as much immunity as an older cow; it often helps to keep them separate from the older cows for at least 2 weeks before they calve.

Mastitis sometimes occurs in baby heifers if infection enters the teats. When raising dairy heifers, a preventative practice is to keep them separate in early life while they are fed milk or milk replacer. Calves that nurse bottles or nipple buckets want to keep sucking after the milk is gone, so they turn to one another and suck each other’s ears or udders.

In cold weather, ear sucking can lead to frozen ears, but even more damaging for a heifer is to have another calf sucking her little teats. Bacteria from the mouth of the sucking calf may enter the teats and cause infection—especially if calves are being fed discarded milk that can’t be sold, such as milk from cows with mastitis.

If a young heifer develops mastitis you may not even know it—until she grows up and has a quarter or two that are non-functional from early damage.

When milking a group of cows, always milk an infected cow last, to reduce the risk of spreading the infection via your hands or milking machine. A good procedure is to milk healthy first calvers, then the healthy older cows, then any cows or heifers that were recently purchased, and lastly any known infected cows.

Always collect any milk you squirt out of the teats ahead of milking; don’t just squirt it on the floor. The highest level of bacteria is in the first milk that exits the teat; squirting this onto the floor of your milk barn will contaminate the environment; the bacteria may be tracked around on human or cows’ feet.

A simple and effective way to help prevent mastitis is use of a good germicidal teat dip after each cow is milked. There are some good commercial products; ask you vet which ones to use. Diluted household chlorine bleach (four parts water and one part bleach) is also effective and kills germs for up to 6 hour or more.

Since the teat sphincter (muscle that opens and closes the opening) is still relaxed right after milking, the teat is vulnerable to invasion by bacteria at that time, especially if there’s still a drop of milk at the end of the teat, providing ideal habitat for bacteria.  A teat dip helps prevent bacterial entrance.

A common practice in dairies is to infuse a long-acting antibiotic into each teat after the final milking when a cow is to be dried up. This will generally get rid of any low-grade chronic infections, and help keep the herd free of mastitis.

Equally important, in a dairy where milking machines are used, is periodic checking of equipment.  If it isn’t functioning just right, teat injury may occur which can lead to mastitis. Minor problems are often overlooked because the equipment is still working, but if it’s working too slowly or loses vacuum, this may lead to teat injury.

The longer the machine is on the teats, the more chance for irritation, which can lead to infection. Proper milking procedures can reduce the incidence of mastitis.


Mastitis should always be treated as soon as you discover it.  The affected quarter should be milked as thoroughly as possible then treated with an antibiotic preparation.  

Mammary infusions for dairy cows work for beef cows also. The antibiotic preparations come in a plastic syringe with a nozzle to insert into the teat opening so you can squirt the medication into the quarter. Some infusions should be given once a day; others work better if given twice daily. The main thing is to keep the quarter milked out if a calf is not nursing it.  

If it’s a beef cow with a suckling calf, it’s usually ok if the calf keeps it milked out unless the cow has a type of infection that would be dangerous to the calf--which is rare.

Often, however, the cow won’t let her calf suckle that quarter because it is sore, and sometimes the calf doesn’t like the taste of the milk. Sometimes there is no milk--just watery fluid.

Milk out as much as you can. It may be lumpy milk or water fluid. After you’ve milked everything out of the quarter, wipe the teat end with a cotton swab and alcohol or use the packaged wipe that comes with the antibiotic product, then inject the medication. Always clean the teat before you inject the medication into it, or you may push more bacteria up into the teat when you insert the cannula.

Milk the affected quarter at least twice a day until the infection clears up and the quarter is producing normal milk again. If the calf will nurse it, this saves you the trouble of milking it out.

Beef cows can be given systemic antibiotics to help clear up mastitis even if you don’t infuse the teats. Beef animals can be given certain antibiotics that you would not give a dairy cow, due to the lengthy withdrawal time before milk from that cow could be used again for human consumption.

Your veterinarian can advise you on appropriate selection of antibiotics, and when and how long to use them. Treatment for a lactating dairy cow is often different than for a cow you will be drying up.
In some instances the veterinarian may want to culture a milk sample to determine which bacteria are involved and choose an antibiotic that might be most effective. Any cow that is dull, off feed, or has a fever should be given systemic antibiotics, whether it’s a beef or dairy cow, or you may lose the cow.

Mastitis can be very serious in some instances, and you’ll want your veterinarian’s advice on treatment for each case. Anti-inflammatory medications may also be prescribed along with the antibiotic.

Diligent and proper treatment can make the difference in whether or not you lose that quarter, or even the cow. If the cow is quite ill, milk her frequently (as often as once an hour) at first, to reduce the level of bacteria and their toxins. Between milkings, use cold packs to reduce swelling and inflammation. 

You can improvise a cold pack using any material that will hold ice or ice-water around the udder, and support it with baling twines or some kind of cord or belting over the cow's back. These measures may help save the cow’s life, slowing the infection/inflammation until the systemic antibiotic has a chance to work.

In instances where gangrene develops, surgical removal of the teat (or even the entire quarter) by a veterinarian may facilitate drainage of toxic materials and increase the chances of salvaging the cow.
Sometimes a dairy cow (and more rarely a beef cow) develops a case of mastitis that won’t respond to standard treatments. Usually the infection is in just one quarter and in these instances the vetrinarian may opt to use a treatment to kill the pathogen and dry up that quarter, so the cow can continue to milk on the other 3 quarters. 

There are a number of products that have been used for this purpose, including infusion of chlorhexadine up into the teat. This will generally kill the pathogen and even though the cow loses milk production from that quarter for the rest of her lactation, the quarter will usually be normal the next time she calves.

Studies of treated dairy cows show that chlorhexadine residues can be detected in milk from the treated quarter for more than 42 days.

Even if that quarter is not milked (allowed to dry up), there are still residues in milk from the untreated quarters for an unacceptable period of time, so use of chlorhexadine in the udder of a lactating dairy (milk for human use) is not a legal treatment.

It can, however, be used in a cow you are going to dry up, or in a beef cow, to salvage the udder in a stubborn case of mastitis.

About the Author

EquiMed Staff

EquiMed staff writers team up to provide articles that require periodic updates based on evolving methods of equine healthcare. Compendia articles, core healthcare topics and more are written and updated as a group effort. Our review process includes an important veterinarian review, helping to assure the content is consistent with the latest understanding from a medical professional.