Dairy cows: Clinical and subclinical mastitis in heifers 

Learn what to look out for when monitoring mastitis in your heifers, including how to spot summer mastitis and how to reduce the risk of coagulase-negative staphylococci (CNS) infections. 

Heifers become susceptible to mastitis pathogens as soon as they begin to produce mammary secretions. Infections can be picked up at any stage between birth and calving. Monitoring mastitis in your heifers allows you to understand the variation and the impact of any control measures.  

It’s important to track:  

• The rate of new high-cell-count infections in heifers – target: less than 10%  
• The rate of new clinical mastitis cases in the first 30 days of lactation – target: less than 1 in 12 heifers affected  

These thresholds give you a starting point for reviewing your current heifer management.  

It’s also important to monitor the types of mastitis infections that may be present. To do this, you should sample individual quarters from affected heifers for bacteriology, using an aseptic technique. Find out how in our Aseptic milk sampling factsheet.  

Sample both:  

• Clinical mastitis cases, before starting treatment  
• High-cell-count quarters in heifers with an increased somatic cell count, identified using the California Milk Test*  

For convenience, you can freeze samples and submit them to a laboratory in batches.  

*See our Dry cow management guide for a step-by-step protocol for the California Milk Test.  

CNS infections are most commonly found immediately after calving, and they’re most likely to have been picked up in the two months prior to calving. To prevent infection, ensure that you provide a clean, dry environment for your heifers and cows throughout the weeks before and during calving.  

The bacteria often establish themselves on teat skin and even in the teat canal, which means there’s also a risk of new CNS infection once heifers come through the milking parlour. To reduce this risk:  

• Ensure you effectively disinfect the teat end during your milking preparation routine  
• Ensure your milking equipment doesn’t damage the teat end   
• Use a post-milking teat dip  

Fresh calved heifers with blind quarters and/or non-functional teats may have been born with this issue, or the damage may have occurred during rearing. If the problem has been present from birth, there may be either:  

• No teat canal, but a teat that fills with milk  
• Less commonly, no milk in the teat and a persistent membrane between the teat cistern and canal at the base of the teat  

A thickened central core in the teat canal may also be caused by summer mastitis, or be the result of damage from being suckled as a calf. The quarter may be dry at calving, or there may be milk in that quarter immediately after calving due to accumulated milk. This quarter later shrinks as it dries off.  

Summer mastitis typically causes a very swollen teat and/or udder shortly before the heifer or cow becomes ill. It most often occurs in summer at pasture, and saving the heifer may require surgical drainage.  

Summer mastitis can be easily identified by careful observation. Look out for the following signs:  

• The affected quarter is very painful, with a thick, smelly yellow secretion on the teat that’s difficult to strip and becomes worse as the disease progresses  
• Flies may become attracted to these unpleasant-smelling secretions  
• As the illness spreads, it affects the entire body and you may notice swelling of the hind legs, obvious lethargy and separation from the herd, with abortion and even death in the most serious cases  
• The heifer may seem lame due to swelling of the udder and hind legs  

If left untreated, the bacterial toxins will damage the udder tissues irreversibly. In many cases, the affected quarter will be lost entirely, or be so badly damaged that it produces very little milk. In serious cases, the battle will be to keep the heifer alive.  

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