Mastitis in Dairy Cows: Causes, Types, Treatment & Prevention — Complete Guide

Mastitis in Dairy Cows: Causes, Types, Treatment & Prevention

The Real Cost of Mastitis — Why This Is Your #1 Dairy Priority

Mastitis is the most economically damaging disease in the global dairy industry. Globally, it costs the dairy sector an estimated $35 billion USD per year in lost milk, treatment costs, early culling, and reduced reproductive performance. For an individual farm, a single clinical mastitis case costs between $200 and $400 depending on severity, lost milk, and the treatment protocol required. Subclinical mastitis — which shows no visible signs — is even more dangerous because it silently reduces milk yield by 5–25% per infected quarter while the farmer remains unaware.

If you are managing dairy cattle — from a two-cow smallholder operation to a 500-cow commercial dairy — mastitis control is the single most profitable area of herd health investment you can make. This guide covers everything you need to understand, diagnose, treat, and prevent mastitis at the farm level.

What Is Mastitis?

Mastitis is inflammation of the mammary gland (udder), almost always caused by bacterial infection. The bacteria enter through the teat canal and multiply within the udder, triggering an immune response. The immune cells (neutrophils) flood into the milk, raising the Somatic Cell Count (SCC) — the primary quality measure used by dairies worldwide.

A healthy cow has an SCC below 200,000 cells/mL. An infected quarter pushes SCC above 200,000, and a cow with clinical mastitis may produce milk with SCC above 1,000,000. Most dairy processors penalise or reject milk above 400,000 SCC — making this a direct financial issue beyond just veterinary costs.

Types of Mastitis: Clinical vs Subclinical

The Most Common Bacteria Causing Mastitis

Understanding which bacteria cause mastitis in your herd is essential for targeted treatment and prevention. The two main groups are contagious pathogens (spread cow-to-cow, mainly during milking) and environmental pathogens (acquired from the cow’s surroundings).

How to Diagnose Mastitis

California Mastitis Test (CMT) — Your Essential On-Farm Tool

The CMT is a rapid, inexpensive test every dairy farmer should perform weekly on individual cows — and daily on high-risk animals (fresh cows, cows with high SCC history). The reagent reacts with neutrophil DNA in milk to produce a gel-like reaction proportional to the SCC level:

• Negative (no reaction): SCC likely below 200,000 — healthy quarter
• Trace/1+: SCC 200,000–400,000 — monitor closely, retest
• 2+ (thick gel): SCC 400,000–1,200,000 — subclinical/early clinical, treat
• 3+ (solid gel): SCC above 1,200,000 — definite clinical mastitis, treat urgently

Milk Culture and Sensitivity Testing

For chronic, recurring, or treatment-resistant mastitis cases, submit a sterile milk sample to your vet for laboratory culture and antibiotic sensitivity testing. This identifies the causative pathogen and guides the most effective antibiotic choice — reducing the risk of treatment failure and antibiotic resistance. Many herds with persistently high SCC have a dominant pathogen that requires a targeted herd-level control programme.

Treatment Protocol for Clinical Mastitis

Step-by-Step Treatment for Mild to Moderate Clinical Mastitis

1. Strip out the affected quarter completely (3–4 strips per milking). Remove infected milk and stimulate natural immune response.
2. Perform CMT or observe abnormal milk in strip cup to confirm which quarter(s) are affected.
3. Take the cow’s temperature — if above 39.5°C, she needs systemic antibiotics and possibly NSAIDs.
4. Administer intramammary antibiotic tubes (licensed for lactating cows). Insert carefully after thorough teat end disinfection.
5. If systemic signs (fever, off feed, dullness) — administer systemic antibiotics and anti-inflammatory drugs as prescribed by your vet.
6. Strip the quarter at every milking. Do not discard post-treatment milk until the stated withholding period has elapsed.
7. Re-examine the cow after 48–72 hours. If no improvement, call your vet for milk culture and revised treatment.

The 5-Point Mastitis Prevention Programme

Evidence from dairy herds worldwide shows that 90% of mastitis infections are preventable through consistent implementation of the five-point programme. This remains the gold-standard protocol recommended by vet schools and dairy advisory bodies globally.

• Post-milking teat disinfection (teat dipping or spraying) — reduces new contagious mastitis infections by 50%.
• Dry cow therapy — treat all quarters at drying off with a long-acting intramammary antibiotic. Prevents new infections during the dry period and cures existing subclinical infections.
• Prompt treatment of clinical cases — never delay. Every day untreated increases damage to udder tissue and infection spread.
• Cull chronic cows — cows with three or more mastitis cases in one lactation, or with SCC consistently above 400,000 despite treatment, should be culled. They are an ongoing infection reservoir.
• Milking machine maintenance — test and service milking equipment every 6 months. Faulty pulsation, excessive vacuum, or liner slip drives teat-end damage and infection entry.

Somatic Cell Count (SCC) Benchmarks — How Does Your Herd Compare?

Frequently Asked Questions

Can a cow recover fully from mastitis?

Mild and moderate clinical mastitis caught early (within 12–24 hours) has a high recovery rate — 70–90% of quarters return to normal production. Severe clinical mastitis or cases left untreated for more than 48 hours may result in permanent tissue damage, reduced production, or loss of the quarter. Gangrenous mastitis requires immediate veterinary treatment and has a poor prognosis for the affected quarter.

What is the milk withholding period after mastitis treatment?

Withholding periods vary by drug, country, and milk market. In the UK and EU, most intramammary antibiotic products carry a 4–8 day milk withholding period. Systemic antibiotics may carry longer withholding periods. Always read the label and record the withdrawal date on your treatment records. Milk tested positive for antibiotic residues at the dairy will result in rejection of the entire bulk tank — a costly event for the whole farm.

How can I reduce mastitis risk in new calving cows?

Fresh cow mastitis is extremely common. Key prevention steps include: correct teat dipping at every milking, ensuring adequate vitamin E and selenium levels (deficiency increases mastitis risk), providing clean, dry calving area bedding, monitoring closely in the first 10 days post-calving, and starting CMT testing from Day 1 post-calving to catch any subclinical infections immediately.