Mastitis means ‘inflammation of the udder', and is usually caused by a bacterial infection. Regarded as the most economically significant infectious disease of dairy cattle, the incidence of clinical mastitis ranges from 32 to 71% with up to 20% of quarters affected in any given period. Mastitis can be classified as clinical; i.e. obvious signs of acute inflammation in the affected quarter and changes in the appearance of the milk, or sub-clinical where the affected quarter appears normal but the milk has an elevated Somatic Cell Count (SCC). Because sub-clinical infection is not easily detected, it often persists in the udder, a condition known as chronic infection.  As a result, the terms "sub-clinical" and "chronic" mastitis are often used interchangeably: both will result in an elevated SCC.

Current requirements from Irish Co-ops are for bulk milk to have somatic cell counts below 400,000. However, for a truly efficient dairy herd the target should be for a cell-count below 200,000. Above this figure indicates the presence of sub-clinical infection and is an indicator of a potentially explosive outbreak in the future. It has been estimated that for each SCC rise of 100,000 above the 200,000 threshold there is a reduction in milk yield of 2.5%. Thus for a cow with an SCC of 400,000 the milk yield is reduced by 5%.  At a milk price of 30 cents per litre, this translates to a reduction in the region of 340 litres or €102 per cow, for a cow with an expected yield of 6,800 litres (1,500 gallons).


Costs associated with mastitis can be divided into four broad areas:

  • Loss of production due to reduced yield
  • Treatment costs
  • Loss of discarded milk due to antibiotic therapy
  • Increased culling
  • Financial penalties for milk with a high SCC

The cost of treating mastitis, with veterinary attendance and drug therapy, contributes to only a small percentage of the overall costs associated with mastitis. Best practice is immediate effective intervention as soon as a mastitis problem is identified. Contact your vet for diagnosis of the type of mastitis and for the most effective treatment and preventative measures. Accurate diagnosis and appropriate therapy will save much greater penalties and losses in the long term.

Prevention & Control

Apply the Internationally recognised "5 point plan"

  1. Hygienic teat management, including wearing disposable gloves when milking, and post milking teat disinfection
  2. Treat all clinical cases promptly with antibiotics and record the details
  3. Cull cows with persistent and repeat cases of mastitis or high SCC as these act as reservoirs of infection within the herd
  4. Dry off all cows with antibiotic dry cow tubes  
  5. Milking machine is to be serviced and maintained. Replace the liners after every 2000 milkings.                            

In addition, good practice includes the following:

  • Checking for signs of mastitis before each milking
  • Monitoring individual cow SCC for signs of sub-clinical infection
  • Good hygiene practices are essential in relation to cows, milking parlour, housing, pasture management and farm staff


Samples should be taken for analysis to identify the causative bacteria, even where it is decided to use a specific intramammary tube or injectable antibiotic on the day of diagnosis to bring the outbreak under control. Knowing the identity of the "bug" often indicates where it is coming from and how it is spreading. Always complete the full course of treatment as prescribed, even when everything appears to be back to normal, and withhold the milk during the period of treatment and for the required time afterwards as stated on the mastitis tube used.

Dry Cow Therapy: Dry cow therapy is an integral part of the well-established 5-point plan and is a vital element in any mastitis control programme.

  • It helps to eliminate existing infections
  • It reduces the risk of new infections
  • By reducing infections it reduces the SCC in the subsequent lactation

The cure rate is the most important attribute of the dry cow tube you use - the higher the cure rate the greater the reduction achievable in lowering somatic cell counts.[1] When costing dry cow therapy, take note of the milk withholding time after calving. 

[1] Marco, J.C. Escobal, I. and Aduriz, J.J. (1995) Efficacy of different dry cow preparations in the control of mastitis. The 3rd International Mastitis Seminar Proceedings, Vol 2, 122-123

[2] Sol & Sampimon, National Mastitis Council Proceedings, (1995)