Get selective with dry cow treatments

A small proportion of intramammary infections will self-cure during the dry period, but the likelihood of cure is greatly enhanced by using antibiotic dry cow therapy.

Antibiotic dry cow therapy has been one of the cornerstones of mastitis management for more than 50 years and has been very successful at reducing the incidence of subclinical intramammary infections.

For decades, we have practised and recommended a ‘blanket’ approach to antibiotic dry cow therapy where all cows received a tube of dry cow treatment per quarter following the last milking of their lactation prior to going ‘dry’.

This was favoured by most veterinarians because it was not only successful at curing many existing subclinical infections but also assisted in the prevention of cows acquiring new intramammary infections in the early dry period.

More recently, the development of non-antibiotic teat sealants, which can prevent cows from acquiring new infections during the dry period, have provided us with an alternative where cows who are unlikely to have an existing intramammary infection are treated with a teat sealant rather than an antibiotic.

This is preferable for several reasons, not the least of which is that it can significantly reduce total antibiotic use on farm.

If new infections can be prevented by providing a non-antibiotic, physical ‘barrier’ to prevent entry of bacteria into the dry udder, this is a great example of good antimicrobial stewardship, and this should be everyone’s aim.

This process of treating cows with a high likelihood of having an intramammary infection with antibiotics, and those who have a low likelihood of having an infection with a teat sealing product is widely known as ‘selective dry cow therapy’.

However, for selective dry cow therapy to be successful, there are several key steps that must be followed.

Data is vital

Firstly, it is essential that sufficient data exists to determine which of the cows that are due to be dried off have a high likelihood of having an existing infection, and therefore will need antibiotic treatment, and which cows are at a low risk of having an existing infection who will be suited for teat sealant only.

In my discussions with farmers who tell me that selective dry cow therapy did not work well for them or even said it was a “disaster”, it is always due to them lacking sufficient information to determine the best treatment for each cow or the application of the selective dry cow protocol was not well managed.

I recommend that for farmers who are interested in selective dry cow therapy that they need to have at least four key pieces of information available:

Making a decision

There is some disagreement between advisers as to what the best cut-off point is below which selective dry cow therapy can begin.

I am of the view that the threshold that is set is quite arbitrary and represents a level of risk that the herd owner is comfortable with.

The lower the ISCC that you use, the less sub-clinically infected cows will escape antibiotic treatment, but the more antibiotics will be used on cows without an infection.

I do not recommend selective dry cow therapy for any cow who has had clinical mastitis during her current lactation, and where possible, I like to review culture results from the clinical cases whenever available.

With more herds either performing on-farm milk culturing or using various technology solutions to assist with treatment decisions, this information is becoming more widely available.

Contagious mastitis pathogens like Streptococcus agalactiae and Staphylococcus aureus may be detected by culturing high cell count cows, clinical cases or from bulk milk surveillance testing.

I do not recommend selective dry cow therapy in herds with contagious mastitis unless significant efforts are made to identify possible carrier animals prior to dry off.

Herds that lack sufficient records, do not have good individual animal ID and lack the management systems to ensure the correct cows are treated with the correct products and withholding and withdrawal periods are able to be observed should not even entertain practising selective dry cow therapy until these problems have been addressed.

Personally, if a herd can tick all four boxes and I believe they are a good candidate for selective dry cow therapy, I recommend that teat sealant only is used in any cow or heifer who has not recorded an ISCC above 150K during the current lactation.

For the cows who are above the threshold, I recommend combination therapy (antibiotic dry cow therapy plus teat sealant).

Getting it right

Lastly, infusion technique is critical to the success of dry cow and teat sealant use.

The teat ends must be spotlessly clean, the correct infusion technique applied (dry cow massaged into udder, teat sealant carefully deposited only into the teat canal) and thorough teat spraying and careful management and monitoring of cows post-infusion is ideal.

If you are unsure if you or your staff are performing this critical task correctly, seek training and advice from your veterinarian

I encourage every dairy farmer to discuss their dry cow plan for the next year with their herd health adviser, determine whether selective dry cow therapy might be suitable for them and if so determine the threshold for treatment with your individual herd veterinarian.

Dr Robert (Rob) Bonanno is the Regional Veterinary Lead for ProDairy in Gippsland and northern Victoria.