Masitis

Masitis is the most common and costly disease of dairy cattle, causing losses from reduced milk production, discarded milk, treatment costs, culling, and death.

By clinical presentation:

• Clinical masitis: Visible abnormalities — swollen, painful, hot quarter; abnormal milk (clots, flakes, watery, bloody); may have systemic signs (fever, anorexia, toxemia)
• Subclinical masitis: No visible abnormalities; elevated somatic cell count (SCC > 200,000 cells/mL); reduced milk production; detected by CMT or SCC testing
• Chronic masitis: Persistent infection; recurrent clinical episodes; often Staph aureus or Mycoplasma; may have fibrosis/palpable quarter changes
• Gangrenous masitis: Severe form with tissue necrosis (blue, cold quarter); E. coli or Staph aureus; may be fatal

By pathogen type:

• Contagious pathogens: Spread cow-to-cow during milking via milker units, hands, or teat skin. Staph aureus, Strep agalactiae, Mycoplasma spp.
• Environmental pathogens: From bedding, manure, soil, water. Strep uberis, E. coli, Klebsiella, Enterococcus, coagulase-negative staphylococci.

California Masitis Test (CMT):

• Screening test for subclinical masitis
• Mix milk with CMT reagent; gel formation indicates elevated SCC
• Score 1 (negative) to 3 (severe); scores ≥ 2 warrant attention

Somatic Cell Count (SCC):

• Normal: < 100,000 cells/mL
• Subclinical masitis threshold: > 200,000 cells/mL
• Bulk tank SCC (BTSCC): Regulatory limit varies (e.g., 400,000 cells/mL in EU; 750,000 in US)

Culture:

• Essential for chronic, recurrent, or severe cases
• Identify pathogen to guide treatment and management (contagious vs environmental)
• No growth = consider Mycoplasma (special media), yeast, or algae

Other diagnostics:

• Palpation: Quarter warmth, swelling, pain, fibrosis
• Milk appearance: Clots, flakes, serous, bloody, purulent
• Systemic signs: Fever, tachycardia, dehydration, shock (severe coliform masitis)

Clinical masitis treatment:

• Antibiotics: Intramammary infusion is first-line for mild/moderate cases. Systemic antibiotics for severe/systemic cases or when Gram-negative suspected.
• Gram-positive (Staph, Strep): Cephalosporins, penicillins, cloxacillin intramammary
• Gram-negative (E. coli, Klebsiella): Often self-limiting; fluids and NSAIDs may be sufficient. Systemic antibiotics if severe.
• NSAIDs: Flunixin meglumine (reduce inflammation, fever, pain)
• Supportive: Fluids, calcium (if down), frequent milking to relieve pressure
• Withholding periods: Observe milk and meat withdrawal times for all treatments

Dry cow therapy:

• Antibiotic intramammary infusion at dry-off for all quarters
• Eliminates existing subclinical infections and prevents new ones during dry period
• Internal teat sealants (orbeseal) can be used alone or with antibiotics

5-Point Masitis Control Plan:

1. Post-milking teat disinfection: Dip or spray teats after every milking (kills pathogens on teat skin)
2. Dry cow therapy: Treat all quarters at dry-off
3. Appropriate clinical therapy: Culture-based treatment, complete course, observe withdrawals
4. Cull chronically infected cows: Staph aureus and Mycoplasma carriers
5. Proper milking machine function: Regular maintenance, correct vacuum, proper pulsation, liners changed on schedule

Additional measures: Pre-milking teat dip (especially for environmental pathogens), good bedding management, clean calving areas, segregation of infected cows, blanket dry cow therapy vs selective based on SCC.