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Targeted approach offers positive outcomes (May 24)

Responsible use of antibiotics requires an evidenced-based approach to target cows that will benefit from treatment – and a name change. A leading specialist mastitis vet tells us more.


Using selective dry-cow therapy is now commonplace on most UK dairy units. When it was first introduced, the approach focused on ‘selecting’ which cows did not require antibiotic dry-cow tubes and, although it is ‘only words’, Devon-based vet Andy Biggs says ‘selective’ is a passive word. He’d like to see producers actively targeting cows that do require treatment.

“As an outward-facing industry, dairying can come under scrutiny and we should be more positive in the description of our approach to the use of antibiotic dry-cow tubes. This should start with a name change.”

He says that a more accurate description of what producers are doing now – identifying cows with a likely intramammary infection that justifies antibiotic dry-cow therapy at drying off – is ‘targeted’ dry-cow therapy (tDCT).

“The word ‘targeted’ is more active and positive than ‘selective’, and it fits with the approach of only using antimicrobials where they are justified by the known or implied presence of a bacterial infection, and that the cow is likely to benefit from treatment.

Teat sealant

“This targets cows suspected of having an intramammary infection. Only these cows are given antibiotic dry-cow tubes, as well as the internal teat sealant at drying off,” says Mr Biggs.

“Decades ago, many of my clients were selecting cows to administer an antibiotic dry-cow tube or not, depending on a perceived need, long before internal teat sealant was introduced in the UK in 2002.”

Selective dry-cow therapy infers that producers are making decisions about which cows don’t require treatment. “Does the industry really want to promote something like that? It suggests that almost all cows will require treatment, if we’re just picking out those that don’t.”

Moving to targeted dry-cow therapy underlines the ‘as little as possible but as much as necessary’ message. Just that one word change puts producers and their vets firmly in charge. Today many cows in the majority of herds only receive a non-antibiotic internal teat sealant (ITS) at drying off, which gives protection against new infections. Producers have also widely adopted the use of ITS on cows that have been given dry-cow therapy to help prevent them picking up a new infection in the late dry period.

The two high-risk periods when dry cows are prone to picking up new infections are during the ‘wet’ period just after drying off and just before calving. ITS, unlike antibiotic dry-cow therapy (aDCT), can offer protection during both periods and can improve overall dry-cow cure rates. This is because it helps ‘capture’ those cows that do cure during the dry period – either by self cure or the result of receiving antibiotic dry-cow tubes – by protecting them from becoming reinfected in the weeks running up to calving.

So how do producers select cows that justify antibiotic tubes at drying off? Two pieces of information are most typically used, according to Mr Biggs: individual cow somatic cell count (ICSCC) and clinical mastitis records for the three months before drying off.

ICSCC should be carried out regularly, either monthly or every six weeks. And in block-calving herds the timing of whole-herd testing, which should be carried out at least three times as the herd approaches drying off, is particularly important.

ITS infusion: first-time users need training

SCC threshold

“Targeting cows to treat should involve a review of the previous three months SCC data and determining if any cows are above the threshold, which is typically 200,000 cells/ml.

“Although a ‘one size fits all’ ICSCC threshold may seem a simple solution, this approach will put many herds, particularly those with a low bulk milk SCC, at risk of treating too many uninfected cows with aDCT. So these herds can use a higher threshold,” says Mr Biggs.

“And herds struggling with a higher bulk milk SCC may find they miss that golden opportunity to cure many unidentified infected cows during the dry period, so these herds should use a lower threshold,” says Mr Biggs.

“Indeed, since the BMSCC and pathogen profile of a herd is likely to change over time, there is a need to continually refresh and re-evaluate the thresholds needed to apply targeted aDCT.”

He adds that it’s also important for producers and vets to watch for cows with a Staph aureus infection, which can ‘hide’ in the udder. “So producers must, again, adapt their targeted DCT approach with this in mind, particularly where Staph aureus has been identified as an issue.”

Producers can also adapt their approach to milking. Many split their herd according to ICSCC, milking so-called ‘dirty’ high-SCC cows after a ‘clean’ lower-SCC group, but there is a better way. “A change in mindset here can also pay dividends and protects ‘clean’ cows from infected herd mates that are ‘borderline’ and could harbour mastitis-causing pathogens,” says Mr Biggs.

“Rather than milking all the cows in the herd that have an ICSCC of more than, say, 400,000 cells/ml, second, as a ‘dirty’ group, milk all the cows with an ICSCC of, say, less than 150,000 or 200,000 cells/ml first, as an elite group.

“As an example of how several cows with SCCs below 400,000 cells /ml could be infected and be a risk to other clean cows, consider a cow with three quarters each with 100,000 cells/ml and one likely infected quarter at one million cells/ml. At testing, her ICSSC at testing would be 325,000 cells/ml.”

Vet discussion

Mr Biggs encourages discussions with the herd’s vet because every herd, system and set-up is different. “Taking a fresh approach and adding some flexibility is usually beneficial. And where SCCs have improved and are now considered good, the targets can be increased to maintain progress in reducing the number of cows receiving aDCT.

“And for herds going through a rough patch with mastitis, possibly struggling with bulk milk SCCs or curing mastitis infections during lactation, a temporary decrease in the threshold – so reducing the SCC limit – could be a smart move. This will ‘bring in’ a few more cows. Cure rates during the dry period are typically twice those seen during lactation. So using targeted DCT on a few more cows could improve cure rates and get the herd back on track in terms of udder health.”

Targeted dry-cow therapy pointers

● Only use antibiotic DCT where it is justified

● Target cows that justify DCT using the previous three months’ clinical-mastitis and ICSSC records, using a threshold agreed with the herd vet

● Inexperienced teat sealant users – get some training. Infusing ITS is completely different to administering antibiotic tubes (see AHDB’s website for technique tips)

● Monitor dry-period performance by looking at ICSCCs before dry off and after calving

● Low SCC is below the 200,000 cells per ml threshold, and ‘high’ is above 200,000 cells/ml

● Dry-period protection = low-low

● Dry-period cure = high-low

● Dry period failure to cure = high-high (the cow may be a candidate for culling)

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