Wednesday, 23 February 2011 13:30

‘Partial insertion’ helps dry-cow therapy

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ONE OF the tools available to dairy farmers to manage mastitis is ‘dry cow therapy’ – intramammary infusion of antibiotics at the end of lactation.

This increases the cure rate of existing infections and reduces the risk of acquiring new infections during the dry period.

Dry cow therapy is a big investment and there are some things that improve its efficacy.

Research work has shown “partial insertion”, i.e. advancing the tip of the dry cow therapy tube only 3mm into the teat canal (rather than right though the teat canal), results in a better cure rate of existing infections.

Additionally, a survey by the writer showed that herds in which ‘partial insertion’ is practised have lower BTSCC in the following lactation, most likely due to getting fewer new infections.

How does partial insertion work? Probably in several ways.

First, the teat canal is lined with keratin, which is part of the first line of defence against invading bacteria. By fully inserting the tip of the antibiotic tube, the keratin layer may be physically removed.

Second, if the teat ends are not properly cleaned and bacteria are carried in on the tip of the tube, these bacteria may be carried all the way through to the cistern, thus bypassing the defences of the teat canal.

Third, full-depth insertion may temporarily stretch the teat canal, making it easier for bacteria to enter.

In contrast, partial insertion leaves a trace of antibiotic in the teat canal, preventing bacteria growing into the teat canal, the first step to infection deeper into the udder.

Practically, partial insertion is easy to do. The tip of the tube is simply partly inserted in the teat canal and the thumb and forefinger of the opposite hand used to clamp the tube tip gently at the teat end. The syringe is then gently plunged so as to prevent any back flow of antibiotic from the teat end.

Products that have a ‘collar’ or ‘two-stage cap’ on the tip – these allow the option of either doing part or full insertion – may make the job of partial insertion easier by having only a few millimeters of the tip exposed, hence preventing the tip being inserted too far.

To get the best out of dry cow therapy, plan to have enough trained people on hand to do the job.

People should be designated to undertake each task. For example, one person might do the teat cleaning (i.e. scrub the teat end with a cotton wool ball moistened with 70% meths), the second might do the dry cow therapy infusion and the third apply teat spray, mark the cows and record the treatments.

Doing the job carefully and consistently will reduce the risk of missing cows, double-treating cows, carrying bacteria into the gland and damaging teats, with the result that the dry cow therapy is more effective.

Don’t rush the job, dry off the herd in groups and budget on doing about 25 cows/person/hour.

Scott McDougall, BVSc, PhD, is a registered specialist in bovine reproduction, is a researcher at Cognosco, the research division of Animal Health Centre, Morrinsville, New Zealand.

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