Dairy cows: Mastitis pathogens in heifers

Mastitis infections occur as a result of pathogens, disease-causing bacteria that infect the udder. Find out about the disease-causing bacteria that lead to mastitis in heifers. 

Back to: Dairy cows – control of heifer mastitis

Understanding the causes of mastitis 

Mastitis pathogens are disease-causing bacteria that establish themselves on the teat and ‘grow’ into the teat canal. Understanding the different types of bacteria that cause mastitis is important in controlling the disease and minimising its impact on your animals and costs. 

Note that the bacteria that cause mastitis in heifers are the same as in dairy cows. Read a summary of major pathogens below and find out more in our detailed guide to mastitis pathogens in older animals. 

Major pathogen infections in heifers 

Environmental mastitis in heifers is most commonly caused by major pathogens, which are the same as in dairy cows, namely:  

  • Streptococcus uberis (Strep. uberis)  
  • Escherichia coli (E. coli) 
  • Klebsiella 
  • Pseudomonas 
  • Trueperella 

The most common major pathogens causing contagious mastitis are also the same as for dairy cows: 

  • Staphylococcus aureus (Staph. aureus) 
  • Streptococcus agalactiae (Strep. agalactiae)  
  • Streptococcus dysgalactiae (Strep. dysgalactiae) 

Read our guides on Control of contagious mastitis and Control of environmental mastitis in lactation for more detail. 

Summer mastitis pathogens 

Summer mastitis is caused by a number of different bacteria, in particular, Trueperella pyogenes and Streptococcus dysgalactiae. Other anaerobic bacteria may also be involved, such as Peptococcus indolicus.  

Note that Trueperella pyogenes causes opportunistic infection all year round, not just in summer.  

Coagulase-negative staphylococci (CNS) 

Coagulase-negative staphylococci (CNS) are a bacterial group commonly found in clinical mastitis cases and in quarters with a high somatic cell count, both in cows and heifers. These infections seem to be more important in heifer mastitis. 

The CNS group consists of over 50 different species and subspecies of bacteria, though only a small number of these are reported as causing mastitis. Some CNS species appear to be more ‘contagious’ and some more ‘environmental’ in terms of their ability to elevate cell count and persist in the udder.  

Research: The impact of CNS infections in heifers 

CNS are associated with a moderate increase in somatic cell count, but may also have a protective role in heifer udder health. Research found that heifers infected with CNS in very early lactation tended to have fewer cases of clinical mastitis throughout lactation compared with non-infected herd mates. Milk yield was also higher in CNS-infected heifers and cows compared with animals not infected. 

Piepers, S., Schukken, Y. H., Passchyn, P., De Vliegher, S. (2013). 'The effect of intramammary infection with coagulase-negative staphylococci in early lactating heifers on milk yield throughout first lactation revisited'. Journal of Dairy Science, 96, pp. 5,095–5,105. 

Useful links

Evaluating heifer mastitis and its costs

Clinical and subclinical mastitis in heifers

Reducing the risk of mastitis in heifers 

If you would like to order a hard copy of the Control of contagious mastitis guide, please contact: Emailpublications@ahdb.org.uk or Telephone: 0247 799 0069