Mastitis is the most common disease of dairy cattle. This video reviews the basics of what causes mastitis, and an overview of how to approach mastitis management. Gain a deeper understanding of its causes, symptoms, effective treatment, and preventive measures.

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  • Mastitis is the inflammation of udder tissue caused by bacteria entering through open teat ends. It is a significant concern for dairy farmers due to its impact on milk production and cow health. By implementing proper management practices, mastitis can be prevented or effectively managed
  • The most common disease of dairy cattle
  • Costs an average NZ dairy herd — $15,000/year1

Prevention and Management

A healthy cow can usually prevent mastitis before any signs appear. Natural defenses against mastitis include:

  • Teat end structure — skin folds close the teat end between milkings preventing bacteria from entering the udder. Ensure proper teat end structure to prevent bacteria from entering the udder between milkings.
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  • Somatic cells (white blood cells)—part of the cow’s immune system, which fight bacteria inside the udder

Somatic cell count (SCC) is a useful indicator of mastitis. It can be measured in an individual cow at herd testing or by RMT, or in an entire herd by bulk milk testing.  Monitor SCC to identify potential cases.

To support the cow’s natural mastitis defenses, you can:

  • Feed her well
  • Reduce stress during handling and milking
  • Keep her teat ends as clean and dry as possible to reduce bacteria at the teat ends
  • Use an efficient milking technique and maintain milking equipment to prevent teat end damage

If mastitis does occur in your dairy herd, it is either:

  • Clinical Mastitis: milk and/or quarter appears abnormal (clots, flakes, swelling, redness, pain, firmness of the quarter)
    • Most common at calving time and early lactation
    • In New Zealand, most clinical cases are caused by environmental bacteria, like Strep. uberis
    • SCC of an infected cow is usually very high
  • Subclinical Mastitis: milk and quarter appear normal, but SCC is elevated
    • SCC of an infected cow may go up and down, but usually stays above 150,000 cells/mL
    • Subclinical infections often go unnoticed
    • Many subclinical infections are caused by contagious bacteria such as Staph. aureus, which spread from cow to cow during milking
    • For any individual cow, subclinical infection can happen at any time of the year
    • On a herd level, subclinical mastitis is more of a problem late in the season, as more cows become infected and milk production decreases


Dairy NZ’s SmartSAMM is a seasonal framework for New Zealand (www.dairynz.co.nz/smartsamm)

Mastitis during calving, focus on:

  • Minimising stress to the cows
  • Practicing good milking hygiene and keeping udders as clean as possible
  • Finding and treating clinical cases ASAP
  • Ensuring all cows entering the milkers have a normal SCC (<150,000 cells/mL)

Mastitis during lactation (after calving is over), focus on:

  • Perfecting the milking technique to limit the spread of subclinical mastitis

Mastitis Dry-off/dry period, focus on:

  • Curing existing infections with antibiotic dry cow therapy (DCT)
  • Preventing new infections with teat sealants and/or management to keep udders clean
  • Culling cows or quarters that are unlikely to cure over the dry period


  1. DairyNZ SmartSAMM. (2018). Mastitis gap calculator. https://www.dairynz.co.nz/animal/cow-health/mastitis/tools-and-resources/smartsamm-gap-calculator/. Assumptions: 414 cows, 381 MS/cow, payout $6.00/kg MS, reduction of SCC from 225,000.
  2. Parkinson, TJ et al. (2010). Calves: management & disease. Diseases of cattle in Australasia: a comprehensive textbook. VetLearn. pp.340–402.


Or find us on YouTube by searching: TopFarmersNZ
Or visit: msd-animal-health.co.nz

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Top Farmers Know-How provides a reference library of industry best practice in some key animal health management areas including mastitis, dry off, calf health, BVD, salmonella and campylobacter. We know that farmers and vets are busy people, so we’ve created resources in different formats and in bite-sized chunks to make it more flexible and accessible.