Mastitis in Dairy Cows: Causes, Symptoms, Treatment, and Prevention

Mastitis in Dairy Cows: Causes, Symptoms, Treatment, and Prevention

Mastitis is one of the most prevalent and costly diseases affecting the dairy cattle industry worldwide. It is defined as the inflammation of the mammary gland and udder tissue, usually caused by bacterial infection. Mastitis can occur in various degrees, from mild to severe, and can become a chronic problem if not treated promptly and properly. Left unchecked, mastitis significantly impacts milk quality and quantity, cow health and welfare, and farm profitability. However, with proactive management, mastitis can be effectively controlled in a dairy herd. This article provides an in-depth overview of mastitis in dairy cows - its causes, risk factors, symptoms, diagnosis, treatment options, prevention strategies, and implications for dairy producers.

Causes and Sources of Mastitis Pathogens

Mastitis occurs when infectious pathogenic bacteria enter the teat canal and multiply in the udder. The four major mastitis-causing pathogens are:

  • Streptococcus agalactiae - A contagious pathogen spread from cow to cow, often during milking. Also known as Strep. ag.
  • Staphylococcus aureus - Also contagious, spread cow to cow. Lives deep in udder tissue making it hard to treat.
  • Environmental streptococci - Opportunistic organisms like Strep. uberis that infect the udder when the cow's immunity is low.
  • Coliforms like E. coli - Enter the teat canal from contaminated bedding or the environment. Cause acute clinical mastitis.

These infectious organisms thrive and multiply in the udder, releasing toxins that damage milk-producing mammary tissue.

There are two main categories of mastitis pathogens:

Contagious Pathogens

Spread from infected cows during the milking process. Main examples are Strep. ag and Staph. aureus. They persist within the udder in chronic infections and need to be specifically treated and controlled.

Environmental Pathogens

Present in bedding, manure, water, and the cow's surroundings. They take advantage of lowered immunity to invade the udder. Examples are coliforms like E. coli and environmental streps. Proper cow hygiene is key to controlling environmental mastitis.

Mastitis Risk Factors

Certain conditions and management factors make cows more vulnerable to mastitis:

  • Dirty bedding - Wet and unclean bedding grows environmental bacteria that can enter teat ends.
  • Teat damage - Cracked skin, steps, frost bite, trauma provide openings for bacteria to enter.
  • Irregular milking schedules - Missed milkings overfill the udder and weaken sphincter defenses.
  • Overcrowding - Allows contagious pathogens to spread. Dirty lounging areas too.
  • Poor hygiene - Unsanitary udders, teats, housing, and milking equipment spread pathogens.
  • Nutritional deficiencies - Weakened immunity if low in vitamin E, selenium, copper, and zinc.
  • Transition period - Hormonal shifts around calving suppress immunity for 1-2 months.
  • Stress - Any factor causing stress such as illness, lameness, heat, social change.
  • Chronic infections - Carriers that don't respond fully to treatment and spread bugs to herd.

The presence of one or more risk factors together with pathogen exposure allows mastitis to develop. Multiparous and high producing cows tend to be most susceptible.

Recognizing Mastitis - Signs and Symptoms

Routine screening along with knowing the signs of clinical mastitis allows early detection and treatment in a herd. Here are indications of mastitis:

Subclinical Mastitis

  • Elevated SCC - Somatic cell count over 200,000 cells/mL indicates subclinical infection. Regular SCC testing finds problem cows.
  • Cowside screening tests - Quick mastitis indicator tests like California Mastitis Test (CMT) react to infection.
  • Milk abnormalities - Appearance changes like flakes, clots, watery milk point to mastitis.

Subclinical cases show no visible symptoms but allow contagious spread and cause production losses. Treating subclinical infections improves herd health and milk quality.

Clinical Mastitis

In contrast to subclinical, clinical mastitis shows obvious visible symptoms:

  • Udder swelling and pain - Inflammation causes hot, tender, swollen quarters or entire udder. Cows reluctant to be milked.
  • Milk abnormalities - Clots, flakes, watery milk, or blood tinged milk due to tissue damage.
  • Reduced milk yield - Drastic drop in production of affected quarters.
  • Systemic symptoms - Fevers over 104°F, lethargy, loss of appetite, dehydration. More severe in coliform mastitis.

Alert and frequent milking personnel may detect clinical mastitis during routine procedures. Severe cases require urgent treatment by a veterinarian.

Diagnosing Mastitis

Diagnostic tests identify the type of mastitis pathogen present to guide treatment and control measures:

  • Bacterial culture - Milk samples cultured in a lab identify causal organisms and antibiotic sensitivities.
  • Polymerase Chain Reaction (PCR) testing - Fast, sensitive DNA-based test detects pathogens from milk samples.
  • Cowside screening - CMT, portacheck, strips quickly indicate mastitis at milking time.
  • Somatic cell count - Monitors udder health status and screens quarters or cows.
  • Ultrasound - Imaging reveals internal tissue changes not visible externally in chronic mastitis.

Once diagnosed, determining the source and patterns of infection directs mastitis interventions for the herd.

Treating Mastitis

Treatment aims to eliminate infection, minimize loss of function, prevent spread, and return to milk production. Options include:


Administered according to sensitivity results, pathogen type, and mastitis severity:

  • Intramammary infusions into the affected quarter/s.
  • Systemic injections for acute, severe mastitis.
  • Extended therapy for chronic staph infections.

Prompt, sufficient dosing is key before tissue is permanently damaged. Discard milk during treatment and withhold periods.


Reduce swelling, pain, and damage to udder tissue. Used alongside antibiotics in clinical mastitis. Includes NSAIDs like Banamine.

Supportive Care

May include:

  • Oxytocin to milk out quarters and relieve pressure.
  • IV fluids, calcium, energy supplements for very sick cows.
  • Applying heat packs to stimulate circulation.
  • Nutritious feeding for recovery.


Cows with repeated chronic untreatable mastitis are culled to improve herd health.

Work closely with your veterinarian to treat mastitis cases promptly and effectively. Follow label drug directions carefully. Keep detailed treatment records on cows.

Preventing Mastitis in Dairy Herds

Since mastitis treatment is difficult and expensive, focusing on prevention is highly cost-effective. Recommended strategies include:

Provide Clean, Dry Housing

  • Regularly replace soiled bedding and add fresh dry bedding.
  • Keep stalls level and well-bedded. Avoid overcrowding.
  • Design barns for good ventilation, low humidity, nodrafts.
  • Use deep sand or saw dust bedding instead of straw.
  • House clinically infected cows separately.

Ensure Proper Milking Hygiene

  • Follow consistent udder prep, cleaning, and teat dipping procedures.
  • Disinfect milking equipment between cows. Routinely maintain and replace inflations.
  • Dip teats immediately after milking with germicidal, emollient dips.
  • Use gloves and clean towels; wash hands between cows.
  • Isolate and milk clinical cases last.

Support Cow Immune Function

  • Meet nutritional requirements for vitamins, minerals, energy that support immunity.
  • Minimize stress; ensure cow comfort.
  • Vaccinate cows to strengthen defenses against common pathogens.
  • Manage transition cows carefully through calving and early lactation.

Dry Cow Mastitis Management

  • Administer intramammary antibiotics at dry off to cure existing infections. Continue teat dipping.
  • Keep dry cows clean, change bedding regularly.
  • Monitor SCC and nutrition status during the dry period.
  • Minimize length of the dry period.

Cull Chronic Mastitis Cows

  • Identify repeat offenders; limit their impact on herd health.
  • Test all cows at dry off, calving, and when sold.
  • Keep herd records of clinical cases, SCC, and antibiotic treatments.

Consistency is vital - establish a schedule and train all farm staff on proper procedures. Monitor herd mastitis status through monthly SCC testing. Work closely with your veterinarian to implement a comprehensive mastitis prevention plan.

Implications and Cost of Mastitis

Mastitis significantly impacts dairy farms by:

  • Reducing milk production - Infected quarters produce less milk; clinical cases see drastic drops.
  • Lowering milk quality - Increased SCC, antibiotic residues, abnormal milk lowers value.
  • Increasing treatment costs - Antibiotics, discarded milk, vet fees, labor to treat cases.
  • Decreased fertility - Mastitis impairs reproductive performance.
  • Culling and death losses - Severe infections result in cows being culled or dying.
  • Spreading disease - Contagious organisms persist and spread without control measures.

Economic surveys consistently identify mastitis as the most costly disease in the dairy industry. Typical total costs range from $100 to over $550 per clinical case, while subclinical infections cost around $110 per cow per year. Adopting proactive prevention practices provides significant returns on investment for dairy producers.


Mastitis will likely remain an ongoing concern for the dairy industry, but its impact can be minimized through vigilant management. Know your enemy - the main mastitis pathogens, their spread, and the tools available for control. Recognize both clinical and subclinical infections promptly. Work closely with your herd veterinarian to treat cases quickly and effectively. And most importantly, consistently follow sound prevention principles every day to build udder health and keep mastitis under control. The rewards will be healthy, productive cows and an improved bottom line.