A Practitioner’s Field Guide to Mastitis Diagnosis

Clinical Mastitis:

1. Acute Clinical Mastitis
   Cows are typically “sick cows with a sick quarter.” The onset is peracute: the affected quarter is hot, swollen, firm-to-hard, and exquisitely painful. Milk is altered from the first streams—serosanguinous, purulent, or frankly clotty. Within 6–12 h the cow is systemically ill: fever ≥ 39.5 °C, rumen stasis, tachycardia, sunken flanks, and dehydration. Capillary refill time is prolonged and milk yield drops sharply. This is a medical emergency; prompt systemic therapy and complete milk-out are mandatory.

2. Sub-clinical / Sub-acute Mastitis
   The cow looks bright and appetent; systemic signs are absent. Milk appears grossly normal on stripping, yet close inspection reveals flecks, clots, or a watery serum separation. The quarter is only mildly warm and doughy on palpation, and pain is subtle. California Mastitis Test (CMT) scores ≥ 2+ or somatic cell count (SCC) > 400 000 cells/mL confirm inflammation. Culture-directed intramammary therapy is indicated before the process becomes chronic.

3. Chronic Clinical Mastitis

   These quarters are the “quiet saboteurs” of udder health. Persistent or recurrent infections (often Staph. aureus, Strep. uberis, or Trueperella pyogenes) drive progressive fibrosis. The quarter is shrunken, fibrotic on palpation, and secretes a thin, serous or intermittently clotted milk. Flare-ups may mimic sub-acute episodes, but between exacerbations the lesion is inapparent. Long-term sequela is permanent loss of secretory tissue and increased risk of super-infection; culling or complete dry-off is frequently the most economical decision.

   Subclinical mastitis is best unmasked with commercial, ready-to-use “cow-side” diagnostic kits (e.g., CMT, DCT, Draminski®). Follow the manufacturer’s strip-well protocol strictly—one squirt of foremilk, one paddle of reagent, one swirl for 10 s. A gel viscosity ≥ 2+ (or color shift if the kit uses chromogenic substrate) equals a positive. Always pair the paddle test with on-farm SCC data: a single quarter SCC > 200 000 cells/mL or a composite ≥ 150 000 cells/mL corroborates the diagnosis and flags the cow for culture-guided therapy.

   Management & Disposition

   Therapy  
   1. Anti-infective therapy  
      - Collect aseptic foremilk samples from every affected quarter before the first antibiotic tube is opened; submit for culture and MIC-based susceptibility testing.  
      - Select the narrowest-spectrum, lactation-approved drug that matches the pathogen’s in-vitro profile (e.g., cephalonium for penicillin-susceptible Staph. aureus, pirlimycin for Strep. uberis, ceftiofur for Gram-negative isolates).  
      - Reserve “critically important” fluoroquinolones and 3rd/4th-generation cephalosporins for life-threatening systemic cases under veterinary oversight.  

   2. Symptomatic relief  
      - NSAIDs (flunixin meglumine 2.2 mg/kg IV q24 h, max 3 days) for fever > 39.5 °C and obvious pain.  
      - Diphenhydramine (0.5 mg/kg IM) if marked udder edema or allergic flare is suspected.  

   3. Adjunctive measures  
      - Peri-mammary procaine-penicillin block (20 mL of 300 000 IU/mL, 4-quadrant deep SC) once daily for 3 days.  
      - Cold hydrotherapy (10 °C water, 15 min) for the first 24 h when the quarter is hot and edematous; switch to warm compress (40 °C) thereafter if fibrosis is palpable.  
      - Strip the quarter every 2–3 h for the initial 24 h to evacuate toxins and enhance drug penetration.  

   4. Milk-withdrawal compliance  
      - Record the exact molecule, dose, route, and time of every treatment; default to the longest published withhold (milk & meat) plus 24 h extra safety margin.  

   Culling decisions  
   - Chronic non-responders: ≥ 3 clinical episodes within the same lactation, or persistently > 1 000 000 SCC in two quarters despite two complete dry-cow cures.  
   - Economically spent cows: projected 305-d yield < 75 % of herd mature equivalent plus recurrent mastitis.  
   - Salvage immediately if flare-ups are accompanied by gangrenous changes or systemic relapse.  

   Milk disposal  
   - All milk collected during the treatment period plus the regulatory withhold must be diverted into a dedicated, clearly labelled “mastitis milk” container.  
   - Hold at 4 °C until collection for acidification or high-temperature rendering; on-farm disposal must meet local environmental standards—never into the bulk tank, never fed to calves.

    

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