Mastitis is the single most costly disease in dairy production. Its clinical and subclinical forms affect nearly every herd. Subclinical mastitis presents primarily as an increase in somatic cell count (SCC) and directly compromises milk quality, yield, and public health. This article reviews mastitis etiology, SCC interpretation, diagnostic tools, treatment protocols, dry cow therapy, and a practical 10-point mastitis control program in light of current literature.
Economic Impact
Mastitis causes an estimated $19.7-32 billion in annual losses worldwide. The cost per case of clinical mastitis is approximately $250-450, while subclinical mastitis may cost $100-200 per cow per year. For every increase of 100,000 cells/mL in SCC, milk yield may decline by 0.4-0.6 kg/day. In Turkey, average bulk tank SCC commonly ranges from 400,000 to 600,000 cells/mL, exceeding the EU limit of 400,000 (Halasa et al., 2007; Seegers et al., 2003).
1. Mastitis Etiology and Classification
1.1 Contagious Pathogens
These pathogens spread from cow to cow, especially during milking. They commonly cause chronic, subclinical infections and lead to persistently elevated SCC.
| Pathogen | Transmission | Clinical profile | Effect on SCC | Treatment response |
|---|---|---|---|---|
| Staphylococcus aureus | Milking equipment, hands | Chronic, subclinical, micro-abscess formation | Very high (>500,000) | Poor (20-30% cure) |
| Streptococcus agalactiae | Milking equipment | Subclinical, raises bulk tank SCC | High | Good (>90% cure) |
| Mycoplasma bovis | Milking, respiratory spread | Multiple quarters, treatment resistant | Variable | None (antimicrobial resistance/lack of response) |
| Corynebacterium bovis | Milking equipment | Mild subclinical infection | Moderate | Good |
1.2 Environmental Pathogens
These organisms are acquired from bedding, manure, soil, and water. They are more often associated with acute clinical mastitis.
| Pathogen | Source | Clinical profile | High-risk period |
|---|---|---|---|
| E. coli | Manure, bedding, water | Acute/peracute, toxemia, fever, shock | Late dry period, early lactation |
| Klebsiella spp. | Sawdust bedding, soil | Acute, severe, high mortality | All stages |
| Streptococcus uberis | Soil, bedding, pasture | Subclinical or clinical, common in the dry period | Dry period, early lactation |
| Streptococcus dysgalactiae | Environmental + contagious | Acute clinical mastitis, good treatment response | All stages |
| Pseudomonas aeruginosa | Contaminated water | Chronic, treatment resistant | Water system contamination |
2. Interpretation of Somatic Cell Count (SCC)
SCC reflects the number of leukocytes, predominantly neutrophils, in milk and is the most reliable indicator of udder health. In a healthy quarter, SCC should remain <100,000 cells/mL (Schukken et al., 2003).
| SCC (cells/mL) | Linear score (LS) | Status | Estimated milk loss |
|---|---|---|---|
| <100,000 | 0-2 | Healthy udder | No loss |
| 100,000-200,000 | 3 | Mild irritation or recovery phase | 0-3% |
| 200,000-400,000 | 4-5 | High probability of subclinical mastitis | 3-6% |
| 400,000-800,000 | 5-6 | Subclinical mastitis (infection confirmed) | 6-10% |
| >800,000 | 7+ | Severe infection | 10-25% |
Bulk Tank SCC Targets
- Excellent: <150,000 cells/mL
- Good: 150,000-250,000 cells/mL
- Acceptable: 250,000-400,000 cells/mL
- Problematic: >400,000 cells/mL (EU legal limit)
- Turkish legal limit: 500,000 cells/mL (raw milk)
3. Diagnostic Methods
| Method | Application | Sensitivity | Main use |
|---|---|---|---|
| CMT (California Mastitis Test) | Foremilk from each quarter mixed with CMT reagent before milking | 70-85% | On-farm screening, low cost, rapid |
| SCC (individual cow) | Monthly DHI milk analysis | 85-95% | Detecting subclinical mastitis, herd monitoring |
| Bacteriological culture | Aseptic milk sample sent to the laboratory | 90-95% | Pathogen identification and treatment selection |
| On-farm culture (Petrifilm, REGA) | Simple culture plates used in the dairy | 75-85% | Gram +/− discrimination and fast treatment decisions |
| PCR | DNA detection from milk samples | 95%+ | Mycoplasma detection, S. aureus typing |
| Electrical conductivity | Milking system sensor | 50-70% | Automated early warning, low specificity |
4. Treatment Protocols
4.1 Treatment of Clinical Mastitis
Treatment Decision: Culture-Based Approach
Modern mastitis therapy favors a "culture first, then targeted treatment" approach rather than treating blindly. On-farm culture that separates Gram-positive from Gram-negative organisms can reduce unnecessary antibiotic use by 40-50%. Most Gram-negative cases, especially E. coli, resolve spontaneously, so supportive care alone (NSAID + frequent milking) is often sufficient (Lago et al., 2011).
| Pathogen group | Treatment | Duration | Cure rate |
|---|---|---|---|
| Gram positive (Strep, Staph) | Intramammary antibiotics (cefoperazone, amoxicillin-clavulanate) | 3-5 days; extended therapy 5-8 days for S. aureus | Strep: 80-90%, S. aureus: 20-30% |
| Gram negative (E. coli) | NSAID (flunixin) + frequent stripping. Systemic antibiotics only with toxemia | 2-3 days of supportive care | 70-85% (many recover spontaneously) |
| Culture negative | No antimicrobial therapy or NSAID alone | — | 80-90% spontaneous resolution |
| Mycoplasma | No effective treatment — isolate or cull | — | 0% (antibiotic resistant/non-responsive) |
4.2 Emergency Treatment of Peracute/Toxic Mastitis
Emergency Treatment: Toxic Mastitis (E. coli / Klebsiella)
- IV fluids: isotonic saline or lactated Ringer's, 10-20 L rapidly
- NSAID: flunixin meglumine 2.2 mg/kg IV to control endotoxemia
- Frequent milking: empty the affected quarter every 4-6 hours
- Systemic antibiotics: ceftiofur 2.2 mg/kg IM or oxytetracycline when indicated
- Intramammary antibiotics: broad-spectrum products such as cefoperazone
- Calcium support: evaluate hypocalcemia and give calcium borogluconate SC when needed
- Prognosis: 70-80% survival with early treatment, but only 30-50% if treatment is delayed
5. Dry Cow Therapy
Dry cow therapy combines intramammary antibiotics with an internal teat sealant at dry-off to treat existing subclinical infections and reduce new infections during the dry period (Bradley et al., 2015).
All cows receive antibiotic therapy plus sealant at dry-off.
- Indication: bulk tank SCC >250,000, high prevalence of S. aureus or S. agalactiae
- Antibiotic: long-acting intramammary products such as cloxacillin or cefalonium
- Sealant: bismuth subnitrate based (e.g. Orbeseal®)
- Advantage: simple and targets all infected quarters
- Disadvantage: unnecessary antibiotic exposure in low-risk cows
Only infected cows receive antibiotics, while all cows receive a sealant.
- Indication: bulk tank SCC <250,000, low prevalence of S. aureus
- Criterion: SCC >200,000 in any of the last 3 DHI tests or recent clinical mastitis → antibiotic + sealant
- Low-SCC cows: sealant only
- Advantage: 40-60% reduction in antibiotic use
- Disadvantage: requires disciplined cow selection
6. Mastitis Control Program: 10-Point Plan
NMC 10-Point Mastitis Control Plan
- Set targets: bulk tank SCC <200,000 and clinical mastitis incidence <2% per month
- Keep housing clean, dry, and comfortable: bedding management and stall hygiene
- Follow proper milking routine: forestripping, teat preparation, timely cluster attachment, avoid overmilking
- Maintain milking equipment: service twice yearly, check vacuum (42-44 kPa) and pulsation
- Post-milking teat dipping: 0.5-1% iodine or 0.5% chlorhexidine
- Treat clinical mastitis: culture-based, protocol-driven, and recorded
- Use dry cow therapy: blanket or selective strategies plus sealant
- Remove chronically infected cows: chronic S. aureus cases or cows with 3+ clinical episodes
- Strengthen biosecurity: test purchased animals and use quarantine
- Monitor and record: monthly DHI, bulk tank SCC, and clinical case logs
7. Milking Hygiene Protocol
| Step | Procedure | Time | Purpose |
|---|---|---|---|
| 1. Forestripping | Strip 2-3 streams from each quarter into a strip cup | 10-15 sec/cow | Detect clinical mastitis and stimulate oxytocin release |
| 2. Pre-dip | Dip teats in disinfectant | 30 sec contact time | Kill environmental pathogens |
| 3. Drying | Dry teats with individual paper towels | 10-15 sec/cow | Remove disinfectant residue and dirt |
| 4. Unit attachment | Attach the unit 60-90 sec after forestripping | — | Match peak oxytocin timing |
| 5. Monitor milking | Avoid overmilking and use automatic take-offs | 4-7 min/cow | Prevent teat-end damage |
| 6. Post-dip | Dip teats immediately after milking | Immediately | Kill contagious pathogens and protect teat condition |
8. Herd-Level Monitoring
| Parameter | Target | Alarm threshold | Measurement |
|---|---|---|---|
| Bulk tank SCC | <200,000 cells/mL | >400,000 | At each collection or weekly |
| Clinical mastitis incidence | <2% per month (cow-month basis) | >4% per month | Monthly records |
| New infection rate during the dry period | <15% | >25% | Compare dry-off and calving SCC records |
| Chronically infected cows (SCC >400,000 for 3+ months) | <5% | >10% | DHI records |
| Clinical mastitis cure rate | >75% | <60% | Post-treatment SCC follow-up |
| Culling due to mastitis | <5% per year | >8% per year | Annual records |
9. References
- Bradley, A. J., et al. (2015). An investigation of the efficacy of a polyvalent mastitis vaccine using different vaccination regimens under field conditions in the United Kingdom. Journal of Dairy Science, 98(3), 1706-1720.
- Halasa, T., et al. (2007). Economic effects of bovine mastitis and mastitis management: A review. Veterinary Quarterly, 29(1), 18-31.
- Lago, A., et al. (2011). The selective treatment of clinical mastitis based on on-farm culture results: I. Effects on antibiotic use, milk withholding time, and short-term clinical and bacteriological outcomes. Journal of Dairy Science, 94(9), 4441-4456.
- NMC (National Mastitis Council). (2017). Current Concepts of Bovine Mastitis (5th ed.). Madison, WI: NMC.
- Schukken, Y. H., et al. (2003). Monitoring udder health and milk quality using somatic cell counts. Veterinary Research, 34(5), 579-596.
- Seegers, H., et al. (2003). Production effects related to mastitis and mastitis economics in dairy cattle herds. Veterinary Research, 34(5), 475-491.