Dairy cows: targeted antibiotic dry cow therapy and treating mastitis in milking cows 

Cure rates for contagious mastitis pathogens during lactation are often poor, but it’s possible to cure over 90% of cases using antibiotic dry cow therapy. This uses narrow-spectrum, long-acting penicillin antibiotics, which can be very effective.  

A number of factors affect how likely you are to achieve a cure during the dry period, the most important being:  

• The age of the cow and history of mastitis cases in the udder  
• The number of affected quarters   
• The somatic cell count (SCC)  

Identifying chronic mastitis can help you decide between treatment and culling, but you should discuss the best way to make this decision with your vet.  

It’s a good idea to monitor actual versus predicted cure rates across the dry period using cell counts. If poor cure rates can’t be explained by high rates of new infection, you should investigate them using culture. Aim for a cure rate in the dry period of 85% or higher, looking for a high cell count in and low out.  

If your herd has a high cell count and a mainly contagious mastitis pattern, consider reducing the threshold for antibiotic dry cow therapy. Use a low SCC threshold and three consecutive monthly milk recordings to increase the chance of identifying infected cows in your herd.  

Don’t use antibiotic injections at drying off or shortly before calving. There’s little evidence to show that this improves cure rates any more than using antibiotic dry cow therapy alone.  

Read more about targeted antibiotic dry cow therapy in our dry cow management guide, and decrease new cases by using the Mastitis Control Plan.  

In herds with a contagious mastitis pattern, it’s important to identify cases of clinical mastitis as quickly as possible. This is because:  

• Early treatment is more effective  
• Early identification and removal of affected cows reduces the risk of both infection spread and increasing bulk milk SCC  

Know the signs  

Check your staff know the mastitis signs they’re looking for and how to respond. Foremilk stripping is the most effective way to identify clinical cases. They should also be looking for swollen quarters, both at cups-on and cups-off. Be extra vigilant during high-risk periods, such as in the first 30 days of lactation.  

If you use in-line mastitis filters, check them regularly. After milking, check the main filter or filter sock for any clots or other irregularities that may indicate clinical signs of mastitis. Also, look out for other problems, such as large amounts of soiling due to bad milking techniques or technical problems with the milking plant. A sudden increase in daily bulk milk cell counts could indicate a missed clinical case.  

Prompt detection (i.e. at milking) and immediate treatment (particularly for the first clinical case in lactation) is important to maximise the chances of cure and minimise the risk of transmission of infection. 

Cows with clinical cases of mastitis must be clearly marked while undergoing treatment. Record all mastitis cases accurately – by cow, quarter and date. 

Segregate affected cows in the milking parlour  

If not milked last, cows with clinical mastitis should at least be milked with a separate cluster. Don’t use this cluster to milk freshly calved cows or to milk cows with milk out of the tank for reasons other than mastitis.  

Agree on a treatment plan  

You’ll need to discuss a mastitis treatment plan with your vet. To help with this, keep good records of clinical cases and regularly review cure rates. It may also be useful to look at antimicrobial resistance patterns for the main bacteria.   

Mastitis caused by E. coli may not need treatment with antibiotics, so discuss this with your vet.  

If it’s the cow’s first case of mastitis in lactation, start treatment with intramammary tubes immediately. In high-cell-count herds, you can delay treating mild and moderate repeat cases (with only a few flecks in the milk and little or no swelling in the udder) while you assess individual cow history and cell count. In this case, it’s important to segregate these cows from the rest of the herd.   

You may decide to use only anti-inflammatories for mild or moderate cases in cows with chronic mastitis that you plan to cull.  

Length of treatment  

One of the most important factors affecting cure is the length of the treatment course, with longer treatment courses more likely to be successful. To ensure a full bacteriological cure, you should finish treatment courses even if the clinical signs appear cured.  

You may be able to improve cure rates by extending intramammary treatment for five to eight days. In most cases, this will be an off-label antibiotic use, and you will need to extend withdrawal periods. Off-label use must be agreed with your vet on a case-by-case basis.  

Injectable antibiotics should not be routinely used to treat mastitis.

Cows with an SCC of over 200,000 cells/ml are likely to be carrying infections. If this applies to more than 10% of the cows in your herd, your farm will have a higher risk of contagious mastitis spread.  

In contagious-pattern herds, it may be reasonable in the short term to treat cows with a high SCC (more than one SCC over 250,000 cells/ml) to reduce mastitis cases and infection pressure. However, it’s not a good strategy for controlling mastitis in the medium or long term.