test for macrocyclic lactone cattle ‘pour-ons’ at 14 days post-drench?? ……. was, Re: cattle drenches, resistance and rotation – a conversation…….

To: WormMail list  (cc LOs; QAAH-L)    WormMail 201005261015

In the previous WormMail (see below), I suggested cattle producers in Australia should check their drenches (‘DrenchCheck’) from time to time by doing a ‘WormTest’ (faecal worm egg count) 7-10 days after treatment.

The reason for  waiting at least 7 days is to allow for gut transit time (time for eggs in the gut at the time of treatment to pass out in the dung) and to make an allowance for ‘egg lay suppression’ (It is known that some anthelmintics can cause female worms to temporarily cease laying).

The reason for the upper limit – 10 days (14 days for sheep) – is the prepatent period of various worms of interest, which, as a rule of thumb, is around 3 weeks.  By prepatent period we mean the time from when the host ingests infective worm larvae until those worms mature, reproduce and pass eggs in the faeces.

In cattle, some Cooperia(small intestinal worm) can have a prepatent period as short as 11 or 12 days. Hence 10 days post treatment as the upper time limit for testing.

But nothing is perfect, and there are various complications.

Paul Mason, well known parasitologist from New Zealand, made this comment:

Post drench testing is fine and laudable, and testing 7-10 days after
treatment with an oral anthelmintic is OK.  But it is not so simple with
a pour-on product.  Following treatment with pour-on MLs there is often a
suppression of egg laying by Ostertagia.  In response to questions at a
farmers meeting some years ago, Barry McPherson (Merial NZ) said to allow
12 days after treatment with IVM for Ostertagia eggs to start reappearing
in the faeces.  Fort Dodge have an example of it taking up to 15 days after
treatment with moxi pour-on.  We try to drench check 13-14 days after
treatment with a pour-on.

So, a test 7-10 days post-treatment is fine for cattle drenches other than pour-on MLs, in which case you should opt for 14 days.

The test is still imperfect and  results suggesting the possibility of resistance should be followed up, with the assistance of your adviser and the manufacturer of the drench you used.


From: Stephen Love/DII/NSW
Date: 24/05/2010 04:00 PM
Subject: cattle drenches, resistance and rotation – a conversation   //    EMAI turns 20  //   Dunning-Kruger: ‘The Triumph of Stupidity’

Cattle drenches, resistance and rotation – a conversation

WormMail 201005241600    WormMail mailing list (recip. undisclosed);  cc LOs, QAAH-L   (‘Apologies if you get this twice, due to list overlap)

The following is a recent conversation with a northern NSW vet whom we will call ‘Alphonse’.

Hi Steve,

I’ve had a producer enquire about rotating cattle drenches as they have used [ a macrocyclic lactone  pour-on ] for a while and were keen to swap to something else.

I explained that resistance is low in cattle worms and that there isn’t a lot on the market that isn’t an ML but has efficacy against Ostertagia.

Do producers in the New England region have a rotational system with drenches? I suppose a lot of them deal with fluke which complicates matters a bit.



Hi Alphonse

I don’t think we should assume resistance is low in cattle worms in Australia anymore, even if we have somewhat less resistance than in NZ, which is likely.   Here is a table I prepared for Turning the Worm (Issue 22, Dec 2007) ) based on papers in the NZ Vet Journal of Dec 2006:

Gareth Hutchinson has given an excellent overview of cattle worm resistance world-wide (Turning the Worm Issues 11 (May 2003) and 12 (December 2003) ) but that is a little dated given developments in NZ (summarised in TTW Issue 22)  and more recently in Australia (field reports of resistance; plus paper by Lyndal-Murphy et al (2010)).

Apart from a couple of published reports by Eagleson and others[1] relating to BZ resistant T.axei (stomach hair worm) in cattle in Australia, and a recent one by Maxine Lyndal-Murphy and others (2010)[2], there has been a dearth of published reports on cattle worm resistance in this country. However the NZ situation with respect to cattle worm resistance has been a wake up call for us (yes, sometimes we can learn things from Kiwis) and in recent years there have been a number of field reports suggesting we have resistance, including ML resistance, in cattle worms in Australia. The question is, how much?

I think Australian cattle producers should start thinking about doing some post-drench testing from time to time, say a worm egg count 7-10 days after treatment. This is not a perfect test, especially in older cattle, but it is at least a start.  By the way, the post-drench worm test should be no longer than 12 days after treatment in cattle as some cattle Cooperia theoretically can have a prepatent period as short as 12 days.

Most people routinely use MLs, especially pour on MLs. And why wouldn’t they? This applies to the New England as well.

It would be better if people didn’t use MLs all the time….   or if they used combinations, e.g. there is an ML+LEV combi drench in NZ (‘Eclipse’) but I don’t think we have one here yet…

BZs and LEV cattle drenches are quite good against Ostertagia except for inhibited stages. LEV has no effect on inhibited Ostertagia and third generation BZs (albendazole, oxfendazole etc) are roughly 80% effective.  Also BZs and LEV cattle drenches don’t have the persistency that MLs have. But persistency can be a two-edged sword.

So, people could use LEV or BZ drenches from time to time if inhibited Ostertagia were not likely to be an issue (e.g. cattle around 18 months old approaching their second/summer autumn – which is when Type 2 ostertagiasis happens in some areas), and if they had some good grazing management to reduce rate of reinfection with Ostertagia (given the lack of persistency of BZs and LEV compared to MLs).

[1] Eagleson JS and Bowie JY (1986). Oxfendazole resistance in Trichostrongylus axei in cattle in Australia. Veterinary Record 119, 604.

Eagleson JS Bowie JY and Dawkins HJS (1992). Benzimidazole resistance in Trichostrongylus axei in Australia. Veterinary Record 131, 317-318.

[2] Lyndal-Murphy and others (2010. Reduced efficacy of macrocyclic lactone treatments in controlling gastrointestinal nematode infections of weaner dairy calves in subtropical eastern Australia. Veterinary Parasitology 168 (2010) 146–150

Veterinarian, state coordinator-internal parasites
Building C02 Northern Ring Rd [Box U86], UNE Armidale, NSW 2351



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