WRML. More on drench resistance of cattle worms

TO: WormMail mailing list (recip. undisclosed) + NSW DPI LOs (Beef).    WRML.201118.More on drench resistance of cattle worms

We have talked before about  cattle worm resistance in Australia. (See links below)

Here is some more information. Following is a summary of a recent field day by Kate Parry, Livestock Officer (Beef Cattle) Wagga Wagga, written in consultation with well known Victorian veterinarian, Dave Rendell.


"Resistance to mectin drenches in cattle is here! – Kate Parry, Wagga Wagga

At a recent field day in Adelong, Dr David Rendell presented some new data highlighting the failure of the chemical active ‘mectin’ to adequately control internal parasites of cattle. Of particular concern was the low efficacy with pour on (backline) versions of the chemical active.

Key messages from Dave’s address are as follows:

Drench resistance in cattle is here!
·        High levels of resistance are present in worm populations to all chemical groups used to control internal parasites in cattle.
·        Resistance to the ‘mectin’ chemical active (when used as an injectable) has been reported at 20% for Ostertagia spp & 40% for Cooperia spp resistance was higher again for ‘pour on’ formulations.
·        Combinations of chemical actives with different modes of action (eg mectin and BZ) can be used to combat emerging resistance issues.
·        Resistance to pour on drenches develops more quickly than injectable or oral drenches.
·        Where resistance is an issue, weight gains of 6 kgs have been reported in mobs of cattle drenched with a combination treatment when compared to a single chemical active.

Drenching cattle is not always required
·        Adult cattle develop strong natural immunity and it is unusual for cattle over three years of age to require drenching.
·        A risk assessment matrix has been developed for producers to determine the need for drenching individual mobs.
·        Some weaners may not require drenching and this can also be assessed using the risk matrix and weight gain as an indicator.

Worm egg counts (WEC) are not always an effective measure of worms in cattle
·        WECs are highly effective tool to determine worms in cattle less than 15 mths of age.
·        WECs in cattle over 15mths are unreliable.
·        WECs are a useful tool in cattle 14 days post drenching to test the efficacy of drenching.

Monitoring weight gain is a good indicator of worm burdens
·        The main effect of worms is a depressed appetite and subsequently a reduced growth rate.
·        Regular weighing and monitoring of cattle growth rate is a very sensitive way to measure the impact of worms.

Dave’s final comments were that in this district due to the relatively low stocking rates (following the drought) it can be difficult to conduct drench trials, since the worm burdens are generally low. Under these conditions drench resistance risk is higher. It is even more important to eliminate unnecessary drenching and to use highly effective drenching products.
Substantial reductions in weight gains must occur before they are observed by the naked eye. Trials have shown farmers are missing out on substantial weight gains due to drench resistance.

NSW DPI in conjunction with LHPA are planning to run a series of workshops to assist producers in developing a plan for internal parasite management in their herds.

If you would like more information about the field day or follow up workshops please contact you local NSW DPI Beef Officer in Wagga Kate Parry on 0458223439. "


Brief comment

While WECs are a useful tool in young cattle for monitoring worm burdens, they can occasionally lead the unwary astray as age-related immunity kicks in more and more (beginning from weaning).  

There have been cases (e.g. work by Eppleston and Watt in the NSW central tablelands) where WECs and/or pepsinogen in cattle post-weaning did not reliably indicate sizable production losses due to worms.

As Rendell intimates in the summary above by Kate, it is a very good idea to regularly weigh cattle as well in order to monitor possible impacts from parasites.

Rendell paper in the Australian Veterinary Journal

David Rendell published his findings on cattle worm resistance in the Australian Veterinary Journal (December 2010).

If you don’t have access to the AVJ, I wrote a summary of Rendell’s findings, and that of others (Lyndal-Murphy et al), in a conference paper, ‘Worms-what’s new’ (2010; see page ix and following).

A copy can be found here:  https://wormmailinthecloud.wordpress.com/2011/11/03/worms-whats-new-conferencejournal-paper-dec-2010-s-love/   or here: http://wormmailinthecloud.posterous.com/worms-whats-new-conferencejournal-paper-dec-2

Combination cattle drenches are coming to Australia

Following NZ’s lead (where, for example, they have an abamectin/levamisole combination), drench companies in Australia are working towards marketing cattle drenches that are combinations of unrelated broad-spectrum anthelmintics.

(See Pubcris at APVMA: http://services.apvma.gov.au/PubcrisWebClient/welcome.do)

Links to some previous ‘WormMails’ on drench-resistant cattle worms




http://www.dpi.nsw.gov.au/aboutus/resources/periodicals/newsletters/turning-the-worm  [ Turning the Worm (Issue 22, Dec 2007)  ]

More data on drench resistant cattle worms in Australia

A survey has been done in Western Australia, and preliminary results from this should be available soon.

Also, PI (Trish) Veale  of Victoria (formerly of Para-Site Diagnostic Services, Benalla) has unpublished data from 2009 which I hope to share (with PIV’s approval) via WormMail soon.

There was also a small study on 6 cattle properties on the North Coast of NSW (Knox M, Love S and Louden S. Unpublished).