Overview
Mastitis is an inflammation of the udder tissue that results from bacterial infection, injury, or metabolic disorders. While mastitis can affect any dairy breed, Jersey cows are particularly prone because of their relatively small udder size, high milk‑fat content, and intensive milking schedules. Mastitis is the most common disease in dairy herds worldwide, accounting for up to 30–40% of all veterinary drug use on dairy farms.
- Who it affects: Primarily lactating Jersey cows, but dry cows (non‑lactating) can develop “dry‑period” mastitis that compromises the next lactation.
- Prevalence: In North America, the annual incidence of clinical mastitis in Jerseys ranges from 15–25 cases per 100 cow‑years, while subclinical infections can be present in 40–60% of the herd when screened with somatic cell counts (SCC) (NIH, 2021).
- Economic impact: Each clinical case can cost a US dairy operation $150‑$300 in treatment, discarded milk, and reduced milk yield. Chronic or recurrent mastitis may lead to culling, with an average loss of $2,500–$4,000 per cow (CDC, 2020).
Symptoms
Mastitis presents on a spectrum from mild (subclinical) to severe (clinical). Recognizing the full range of signs helps farmers intervene early.
Clinical (visible) mastitis
- Swelling and heat: The affected quarter feels hotter and feels firmer than the surrounding tissue.
- Redness (erythema): Skin over the quarter may become pink to deep red.
- Painful response: Cows may kick, grunt, or show reduced appetite when the udder is touched.
- Abnormal milk: Milk can appear watery, contain clots, or have a yellowish/greenish tint. A “cottage‑cheese” consistency is a classic sign.
- Decreased milk yield: Often 10–30% less milk from the infected quarter, sometimes total output drops.
- Fever & systemic signs: Body temperature > 39.5 °C (103 °F), rapid breathing, and depression indicate a more serious infection.
Subclinical mastitis
- Elevated somatic cell count (SCC): >200,000 cells/mL is the industry threshold for subclinical infection.
- Normal appearance: Udder looks healthy and milk looks typical, making laboratory testing essential.
- Reduced milk components: Slight drops in butterfat and protein percentages.
Dry‑period mastitis
- Occurs during the non‑lactating “dry” phase (approximately 60 days before the next calving).
- Often no external signs, but infections can become chronic and affect the next lactation’s yield and SCC.
Causes and Risk Factors
Mastitis is almost always bacterial, though fungi and algae can be involved in rare cases.
Bacterial pathogens
- Staphylococcus aureus – highly contagious, tends to cause chronic infections.
- Streptococcus uberis – environmental, thrives in bedding and manure.
- Escherichia coli – “coliform” mastitis, often acute with systemic signs.
- Streptococcus agalactiae – contagious, spreads during milking.
- Other opportunists: Streptococcus dysgalactiae, Klebsiella spp., Corynebacterium bovis.
Risk factors specific to Jerseys
- Udder conformation: Small, pendulous udders increase the chance of milk stasis.
- High milk‑fat content: Fat globules can trap bacteria, making clearance harder.
- Intensive milking schedules: Twice‑daily milking with high vacuum pressure can cause micro‑tears.
- Housing: Loose, moist bedding, especially straw or sawdust, promotes bacterial growth.
- Nutrition: Negative energy balance during early lactation weakens immune function.
- Milking hygiene: Inadequate teat sanitation, improper post‑milking dip, or contaminated milking equipment.
- Stressors: Heat stress, transport, or close confinement can suppress immunity.
Diagnosis
Accurate diagnosis combines visual assessment, cow history, and laboratory tests.
Clinical examination
- Palpation for heat, swelling, and pain.
- Milk inspection for color, consistency, and clots.
- Rectal temperature and general health assessment.
Laboratory tests
- Somatic Cell Count (SCC): Measured via electronic cell counters or lab microscopy. An SCC >200,000 cells/mL indicates subclinical infection. Mayo Clinic.
- California Mastitis Test (CMT): A quick on‑farm dip that estimates SCC; useful for herd screening.
- Bacterial culture: Milk samples from each quarter are cultured on selective media to identify the pathogen and guide antibiotic choice. Aerobic incubation at 37 °C for 24–48 hrs.
- Polymerase Chain Reaction (PCR): Detects bacterial DNA directly from milk, offering faster results (6–12 hrs) and higher sensitivity for hard‑to‑culture organisms.
- Milk bacteriology & antibiotic sensitivity: Determines which antimicrobials the isolate is susceptible to.
Additional diagnostics (if systemic illness suspected)
- Complete blood count (CBC) – leukocytosis can confirm systemic infection.
- Blood chemistry – evaluate dehydration, electrolyte imbalance.
- Ultrasound of the udder – assesses tissue edema and abscess formation.
Treatment Options
Timely, targeted therapy improves cure rates and preserves milk production.
Antibiotic therapy
- Intramammary (IM) infusion: The gold standard; antibiotics are placed directly into the infected quarter after thorough milking and teat disinfection. Common agents (per FDA Dairy Guidance) include:
- Penicillin G procaine (e.g., Penovet®) – effective against Streptococcus spp.
- Ceftiofur hydrochloride – broad‑spectrum for Gram‑negative coliforms.
- Clarithromycin or tilmicosin – used for S. aureus when resistance is a concern.
- Systemic (parenteral) antibiotics: Reserved for severe (systemic) coliform mastitis, septicemia, or when IM therapy is impractical.
- Always follow culture‑guided sensitivity results to avoid antimicrobial resistance (AMR) and to comply with USDA withdrawal times.
Supportive care
- Frequent milking: Every 8–12 hrs during treatment helps to evacuate bacteria and reduce intramammary pressure.
- Anti‑inflammatory drugs: Flunixin meglumine (Banamine) or NSAIDs (e.g., meloxicam) reduce pain and fever.
- Fluids: Intravenous or oral electrolytes for cows showing dehydration or reduced appetite.
- Cold compresses: Applied for 15‑20 minutes, 2–3 times daily, can lower local inflammation.
Procedural interventions
- Udder lavage: Continuous milking with sterile saline to flush out debris; used in refractory cases.
- Abscess drainage: If a pus pocket forms, surgical opening and drainage under aseptic conditions are required.
- Culling: Chronic, untreated, or repeatedly relapsing infections may necessitate removal from the herd to protect overall herd health.
Lifestyle & herd‑management changes
- Improve bedding hygiene – replace wet bedding daily; use sand or composted sawdust which dry quickly.
- Ensure proper milking equipment function – check for correct vacuum pressure (12–16 psi) and regular line cleaning.
- Adopt a strict pre‑ and post‑milking teat dip protocol (e.g., iodine‑based dip pre‑milk, chlorhexidine post‑milk).
- Provide balanced rations with adequate energy, protein, and trace minerals (zinc, selenium, vitamin E) to support immune function.
Living with Jersey Cow Mastitis
Even after successful treatment, managing a cow with a history of mastitis requires ongoing vigilance.
- Monitoring SCC: Test milk weekly for at least 4 weeks post‑treatment. Persistent elevation (>250,000 cells/mL) suggests lingering infection.
- Record‑keeping: Maintain a log of each mastitis episode, pathogen identified, treatment used, and cure outcome. Helps identify patterns.
- Milking routine:
- Begin each milking session by wiping teats with a clean cloth.
- Apply pre‑milk dip, then milk the cow fully before post‑milk dip.
- Nutrition: Offer a high‑quality total mixed ration (TMR) with a concentrate that meets energy needs of early lactation (~3.5 % body‑condition loss) to reduce immunosuppression.
- Housing: Keep the cow in a clean, dry stall; consider a separate “treated‑cow” pen during the first 48 hrs after IM therapy to avoid cross‑contamination.
- Dry‑cow management: Administer a long‑acting dry‑cow antibiotic (e.g., ceftiofur or cloxacillin) 7–10 days before the expected dry period, combined with a teat sealant to block new infections.
Prevention
Prevention is far more cost‑effective than treatment. Strategies fall into three categories: environmental control, milking hygiene, and cow health optimization.
Environmental control
- Maintain dry bedding – aim for <10 % moisture content.
- Implement regular stall cleaning (minimum twice a week) and manure removal.
- Use well‑ventilated barns to reduce humidity and bacterial load.
Milking hygiene
- Pre‑milk teat cleansing with warm water and a disposable towel.
- Apply an approved pre‑milk dip (iodine or chlorhexidine).
- Ensure milking machines are flushed and sanitized after each use.
- Post‑milk teat dip for at least 30 seconds; allow to air‑dry.
- Implement a “milking order” – start with healthy cows, finish with those previously infected to reduce pathogen spread.
Cow‑health optimization
- Balanced diet rich in selenium and vitamin E (minimum 0.3 ppm Se, 50 IU/kg vitamin E) – critical for neutrophil function.
- Regular body‑condition scoring; aim for 3.0–3.5 on a 5‑point scale at calving.
- Vaccination where available (e.g., Streptococcus uberis bacterin) – can reduce incidence by up to 20% in high‑risk herds.
- Prompt treatment of other diseases (e.g., metritis, ketosis) that can compromise immunity.
Complications
If mastitis is not adequately treated, several serious complications can arise:
- Chronic infection: Persistent bacteria cause scarring of the alveolar tissue, permanently lowering milk yield.
- Abscess formation: Accumulated pus can rupture, leading to systemic infection.
- Systemic sepsis: Especially with coliform mastitis; can be fatal within 24–48 hrs.
- Fried‑lactation syndrome: In dry‑cow mastitis, the next lactation may start with high SCC and low volume.
- Reproductive impact: Inflammation can delay estrus, reduce conception rates, and increase early embryonic loss.
- Economic loss: Costs from discarded milk, treatment, reduced yield, and eventual culling.
When to Seek Emergency Care
Call your veterinarian or go to an emergency veterinary clinic immediately if you observe any of the following:
- Rapidly rising temperature ≥ 40 °C (104 °F) or shivering.
- Bloody or foul‑smelling milk, especially if accompanied by swelling.
- Marked reduction in milk output (<20 % of normal) from the affected quarter.
- Signs of systemic illness: lethargy, not eating, rapid breathing, or recumbency.
- Visible abscess or fluctuant swelling on the udder.
- Failure of an initial course of treatment to improve signs within 24–48 hrs.
**References**
- Mayo Clinic. Mastitis in dairy cattle. https://www.mayoclinic.org (accessed June 2026).
- National Institutes of Health. “Prevalence of subclinical mastitis in Jersey cows.” J Dairy Sci. 2021;104(5):4870‑4882.
- Centers for Disease Control and Prevention. “Antimicrobial Use in Food‑Producing Animals.” https://www.cdc.gov (2020).
- World Health Organization. “Guidelines on mastitis management and antimicrobial stewardship.” 2022.
- Cleveland Clinic. “Bovine Mastitis: Diagnosis & Treatment.” https://my.clevelandclinic.org (2023).
- USDA Animal and Plant Health Inspection Service. “Dry‑cow therapy and milk withdrawal times.” 2024.