Treating mastitis in cows starts with identifying the type of infection, then combining antibiotic therapy with supportive care and prevention measures to protect the rest of the herd. The approach differs depending on whether you’re dealing with a mild clinical case, a severe systemic infection, or a subclinical problem that only shows up in somatic cell counts. Getting the diagnosis right before reaching for antibiotics saves money and reduces unnecessary drug use.
Identify the Type of Mastitis First
Mastitis falls into two broad categories based on where the bacteria come from. Contagious pathogens like Staphylococcus aureus and Streptococcus agalactiae spread from cow to cow, typically during milking. Environmental pathogens, including E. coli, Klebsiella, and various streptococcal and staphylococcal species, come from bedding, manure, and soil. The distinction matters because contagious infections tend to become chronic and subclinical, while environmental infections often hit hard and fast with visible symptoms.
You also need to distinguish between clinical and subclinical mastitis. Clinical mastitis produces obvious signs: swollen quarters, abnormal milk (clots, watery consistency, discoloration), and sometimes fever or loss of appetite. Subclinical mastitis shows no visible changes in the udder or milk but quietly raises somatic cell counts and reduces production. Subclinical cases are far more common and collectively cost more in lost milk than clinical flare-ups.
Use the California Mastitis Test for Quick Screening
The California Mastitis Test (CMT) is a simple, cowside screening tool that estimates the white blood cell concentration in milk from each quarter. You squirt a few streams of foremilk into a paddle, add the reagent, and swirl. The degree of gel formation tells you the severity:
- Negative: Liquid stays fluid, no thickening. Cell count below 200,000 per milliliter.
- Trace: Slight precipitate that disappears with swirling. Roughly 150,000 to 500,000 cells/mL.
- Score 1: Distinct thickening but no gel. Around 400,000 to 1,500,000 cells/mL.
- Score 2: Clear gel forms in the paddle. Between 800,000 and 5,000,000 cells/mL.
- Score 3: Strong gel that peaks in the center and sticks to the paddle. Over 5,000,000 cells/mL.
A score of 1 or higher in any quarter warrants attention. The CMT won’t tell you which bacterium is involved, though. For that, you need a milk culture, either on-farm using simple plates or through a diagnostic lab. Knowing the pathogen helps you choose the right antibiotic and decide whether treatment is likely to work at all.
Antibiotic Treatment for Clinical Cases
Intramammary infusion is the primary route for treating mastitis during lactation. Several antibiotics are FDA-approved for this use, spanning penicillin-type drugs, cephalosporins, and other classes. Your veterinarian will recommend a specific product based on culture results and herd history. Some products are available over the counter while others require a prescription, and each carries a different milk withdrawal period, ranging from 36 to 96 hours depending on the drug.
The withdrawal period is the minimum time you must discard milk after the last treatment before it can enter the bulk tank. Violating withdrawal times risks antibiotic residues in milk, which creates legal and food safety problems. The federal legal limit for somatic cell count in cow milk is 750,000 cells/mL, and milk with residues will be rejected entirely. Keep detailed treatment records for every cow, including the drug used, date, and the calculated safe-to-ship date.
Not every case of clinical mastitis needs antibiotics. Mild cases caused by E. coli and other gram-negative bacteria often resolve on their own within a few days because the cow’s immune system clears the infection. Culture-based treatment decisions, where you collect a sample before starting therapy and only use antibiotics when the culture confirms a responsive pathogen, can cut antibiotic use significantly without hurting cure rates. Cases caused by Staph. aureus, on the other hand, have notoriously low cure rates during lactation, especially in older cows with chronic infections. Sometimes the best decision is to mark the cow for culling rather than spending money on repeated treatments that won’t work.
Anti-Inflammatory Support
For moderate to severe clinical mastitis, anti-inflammatory medication reduces pain, fever, and udder swelling. Flunixin meglumine is the most commonly used option in cattle, given intravenously at a dose based on body weight. It’s approved only for intravenous use in cattle, not intramuscular, which is important because giving it by the wrong route causes tissue damage and violates label requirements.
Frequent stripping of the affected quarter, milking it out every few hours, helps flush bacteria and inflammatory debris from the udder. Some producers also use hydrotherapy (warm or cold compresses on the udder) for comfort, though the primary benefit is from getting the infected milk out as often as practically possible. Keeping the cow hydrated and eating is critical, especially in severe coliform mastitis where cows can become toxic and go off feed rapidly.
Dry Cow Therapy
The dry period, when a cow stops being milked before her next calving, is one of the best windows for curing existing infections and preventing new ones. Historically, every cow in the herd received intramammary antibiotics at dry-off, a practice called blanket dry cow therapy. This approach made sense when contagious mastitis organisms were widespread, but herds with good udder health can now use a more targeted strategy.
Selective dry cow therapy identifies which cows actually need antibiotics at dry-off and which ones only need an internal teat sealant. The decision is based on the cow’s mastitis history during the lactation and her somatic cell count records. Cows that had clinical mastitis events or recorded somatic cell counts above 200,000 cells/mL get both antibiotics and a teat sealant. Cows with clean records get the teat sealant alone. For herds that want even more precision, culturing a composite milk sample before dry-off can identify cows with hidden infections. The culture doesn’t need to identify the specific pathogen; simply detecting any bacterial growth is enough to flag a cow for antibiotic treatment.
Internal teat sealants are non-antibiotic products that form a physical plug in the teat canal, mimicking the natural keratin plug that forms during the dry period. They’re highly effective at preventing new environmental infections during the weeks when the udder is most vulnerable.
Prevention Through Milking Hygiene
Treatment without prevention is an endless cycle. The milking routine is your first line of defense against contagious spread. Pre-dipping teats with a disinfectant, wiping them dry with individual towels (one per cow), and applying a post-milking teat dip after every milking session are the basics. Post-milking teat dips typically use iodine-based solutions at concentrations around 0.25% iodine. The amount of free iodine in the solution, which determines how quickly it kills bacteria on the teat skin, varies between products and affects efficacy.
Milking equipment also plays a role. Pulsation failures, excessive vacuum levels, and liner slips can damage teat ends and push bacteria into the udder. Regular system checks, at least twice a year by a qualified technician, catch problems before they cause outbreaks.
Bedding and Housing Choices Matter
The material your cows lie on directly affects their exposure to mastitis-causing bacteria. Research comparing bedding types in freestall housing found meaningful differences. New sand bedding performed best: 81% of subclinical mastitis samples from cows on new sand showed no significant bacterial growth, compared to only 46% for cows on shallow-bedded manure solids over mattresses. Recycled sand fell in between, with 59% of samples showing no growth.
Deep-bedded new sand supports fewer bacteria because it drains well and stays drier than organic materials. Manure solids, while cheaper, provide a rich growth medium for environmental pathogens. If sand isn’t practical for your operation, keeping organic bedding clean, dry, and frequently replaced is the next best approach. Stalls should be raked or groomed at least twice daily, and wet spots in the back third of the stall where the udder rests need the most attention.
Beyond bedding, overcrowding increases mastitis risk by forcing cows to lie in alleys and dirty areas. Adequate ventilation reduces humidity and heat stress, both of which suppress immune function and promote bacterial growth on teat skin.
Monitoring Herd Health Over Time
Tracking somatic cell counts at the herd and individual cow level is the most reliable way to measure whether your mastitis control program is working. Monthly Dairy Herd Improvement (DHI) testing gives you individual cow SCC data that you can trend over time. A bulk tank SCC consistently below 200,000 cells/mL indicates a well-managed herd. Counts creeping above 400,000 signal a developing problem, and anything approaching the federal limit of 750,000 cells/mL means the situation is urgent.
Culture every clinical case before treatment when possible. Over months, the pattern of pathogens you’re seeing tells you whether your problem is contagious (spreading at milking time) or environmental (coming from housing), and that distinction drives completely different management responses. A herd dominated by Staph. aureus needs milking order changes and culling decisions. A herd full of E. coli cases needs better bedding and stall management. Treating the symptoms without addressing the source guarantees the problem comes back.