How can dry cow therapy reduce the need for antibiotics on farms?

Take home messages:

- Selective dry cow therapy is straightforward to implement on farm and will reduce antibiotics use. If you have a high incidence rate of mastitis in your herd, veterinary advice should be sought.

- Teat sealants are a useful tool to reduce the likelihood of quarters which are healthy at dry-off becoming infected in the dry period, and should reduce your mastitis rate in the next lactation without having to use antibiotics

The dry period is crucial in the lactation process. It gives time for the udder lining to repair, and allows for optimal milk production in the next lactation.

Within the repair process, milk secretion dries up, the udder lining gets smaller and reduces activity, and a keratin plug forms in the teat canal.

The dry period is also a time to clear up any mammary infections. Previous cases of clinical or subclinical mastitis can be treated and new infections prevented. 

Prevention of new infections from environmental bacteria in the dry period is imperative as these can become clinical cases after calving. 

It may seem odd that there is still a risk from bacteria getting into the teat whilst there is a keratin plug present, however the formation of the plug may be delayed, and cows are more susceptible to infection in the initial period after drying off. 

Furthermore, in high yielding dairy cattle, milk leakage can occur meaning that the teat is not effectively sealed - these animals are reported to be four-times more likely to get an infection.

Blanket dry cow therapy (BDCT) has been a standard method for both treatment and prevention in the dry period. This method uses antibiotics in all quarters of all cows in the herd at drying off.

During the dry period, higher doses can be used than when the cow is in milk, and the flow of milk at milking will not flush the antibiotic out. 

However, by blanket treating the herd with antibiotic dry cow therapy there will be many cows in the herd that are treated with antibiotics when they don’t need it. 

Antimicrobial resistance is a real problem in human and veterinary medicine and we are running out of options. Therefore, the whole of the agricultural sector needs to do its best to reduce the use of antibiotics as much as possible, without impacting animal health and welfare. 

Dairy cow
What is selective dry cow therapy?

SDCT is the treatment of cows with antibiotics based on an assessment of the presence of an intra-mammary infection before drying off – usually determined through somatic cell counts. 

This method can be administered at the cow or quarter level, though it is likely more easily implemented at the cow level in practice.

What should be done about the cows that don’t receive antibiotics and how do we prevent any new infections during the dry period?

Teat sealants with or without antibiotics are becoming more common in dry cow management, with internal sealants being favoured over external sealants. 

Internal sealants are infused into the teat canal and act as a barrier to any invading environmental bacteria. The sealant is a paste which will stay intact in the teat in the presence of milk and is stripped out at the first suckling or stripping out post calving. 

When somatic cell counts are low before dry off and there is no history of mastitis in the previous lactation, there has been shown to be no benefit to using antibiotic treatment over teat sealants alone. 

Further to this, there are a number of research studies which have shown that the use of teat sealants - when applied correctly - in the dry period reduces the prevalence of mastitis in the subsequent lactation. 

How can I implement SDCT on my farm?

You and your vet will need to decide on strict selection criteria - the most common selection tool is SCC. The current advised cut-off is 200,000 cells/ mL. 

Any cows that have SCC equal to or over this level should receive antibiotic treatment and a teat sealant and those with less and no history of clinical mastitis should only receive teat sealants. 

Use of SCC as a selection method and the consideration of incidents of clinical mastitis in the previous lactation will give a fairly good accuracy for selecting uninfected cows to receive teat sealants alone, although this could be improved on through other methods.

What should I do if I have a high percentage of cows with SCC >200,000 cells/mL?

On farms with a high prevalence of mastitis the majority may still need antibiotics, so there will be limited room to reduce antibiotic use. 

On these farms the overall herd management should be looked at to identify any areas for improvement targeted to reduce the mastitis prevalence. 

Practices such as improvement of housing and udder cleanliness milking hygiene and milking equipment being in good repair may be a useful place to start. 

Disease management should always involve discussions with your vet. Once the cases of mastitis in the herd are reduced, use of antibiotics within the dry period should be required less and a SDCT regime could be implemented.

Read the full article 
Article published with the kind permission of Farming Connect

By Dr Ruth Wonfor: IBERS, Aberystwyth University
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