WRML. Drench resistance tests in the Wagga area (eastern Riverina) NSW (Hume LHPA) + sundry

To WormMail mailing list

Drench resistance tests (sheep) – Wagga Wagga area, southern NSW

Many of you receive WormBoss News each month and will have seen this:

Amy Shergold, Wagga Wagga, (amy.shergold) and Tony Morton, Wagga Wagga (tony.morton) – Hume LHPA

"The hot dry conditions of late spring and early summer saw a return to good conditions for worm control. Unfortunately while good for worm control, the hot, dry, windy weather was also associated with bushfires and loss of pasture quality.

A number of drench resistance trials were conducted across the Hume region last year. Qualitative results for eight properties near Wagga Wagga are shown below:

Property Moxidectin Ivermectin Lev/BZ Triple Rametin/
1 R R
2 R
3 R R
4 R
5 R R R
6 R R
7 R R
8 R

R = resistance (<95% overall efficacy); — drench not used in trial Lev = levamisole BZ=benzimidazole Triple = a macrocyclic lactone (ML) active+BZ+Lev Rametin = naphthalophos Abamectin/derquantel is ‘Startect’ (Pfizer): not yet available in Australia. (‘Not sure why that column is blank. Top secret? – SL)

Ivermectin resistance was found on all eight properties and overall efficacy ranged from 15 to 83%. The resistant worm species varied between farms but included Ostertagia (small brown stomach), Haemonchus (barber’s pole) and Trichostrongylus (black scour) worms. The emerging issue of ivermectin resistant Trichostrongylus species was seen on five of eight properties based on larval examination. This general trend was also consistently repeated in similar trials conducted from our other offices at Albury and Gundagai. On the whole moxidectin performed well; however, in light of the profound ivermectin resistance it should be used prudently. Resistance to white/clear combinations remains common as expected.

These results should help those individual producers concerned with their drench rotations. What happens when you combine a drench test, use of an effective product and good farm management? An example is a property where the six ewe mobs were drenched in early November as pasture hayed-off with a drench proven to be effective on that property; the highest count in six mobs monitored in early January was only 32 epg."

Comments (SL):

*Resistance is so widespread now (see here) it is even more essential ! (yes, a tautology) for each producer to test and see what drenches work on their property. See here.

*Ivermectin might be a good benchmark for doing resistance tests but is no longer recommended (on its own, or in combinations) for use in sheep in Australia, because resistance to the macrocyclic lactones (MLs, mectins) is now quite widespread, and ivermectin, the first of the MLs to be launched, is the least potent of them. If you are going to use a short-acting ML, then abamectin is a better choice, because it is more potent (better at killing resistant worms). And, if you are going to use abamectin (or any other drench), seriously consider using it in combination with an other unrelated drench active(s). Why? : efficacy and resistance management.

* Resistance of Trichostrongylus (black scour worm; stomach hair worm; "Trichs") has been slower to appear than that of Haemonchus (barber’s pole worm) and Ostertagia (Teladorsagia) (small brown stomach worm). There is more and more field evidence that ML-resistant ‘Trichs’ are no longer rare. A sticking point is that few field cases have yet to be confirmed by identification of adult worms. Identification of ‘Trichs’ vs ‘Osties" based on larvae is not 100% reliable.

* If there is so much resistance ‘out there’ – and there is! – more farmers have to be fair dinkum about biosecurity when it comes to keeping out resistant worms (and other things e.g. OJD, footrot, drug-resistant lice etc). See here and here (information on ‘quarantine"):

* It’s better to use unrelated drench actives in combination than in a rotation. But, you can rotate combinations eg. in no particular order: a naphthalophos-based triple combination (NAP + BZ +LEV), then ‘Zolvix’ (monepantel), or ‘Startect’ (abamectin+derquantel; when it becomes available), then a ML-based triple (e.g. ML+BZ+LEV). OK, not all actives are being rotated, but some are. (Nothing is perfect, me and thee excepted). Get advice on the best approach for your situation.

‘Sounds expensive? The most expensive drench is the one that doesn’t work, or the one that was unnecessary (i.e. a WormTest would have shown that a drench was unnecessary).

* Don’t guess, WormTest.

A case in point (the simplified version) : A colleague is working with a producer [in a barber’s
pole worm
endemic area] who has about 5000 Merino weaners. Has been ‘burnt’ in the past by barber’s pole worm. He is itching to get into these weaners and drench them. My colleague persuaded the producer to do a WormTest. The highest egg count was 240 eggs per gram of faeces (epg), there were quite a few zeros, and the average strongyle epg was 84. Larval culture indicated most of the worms were barber’s pole worm. This is a very low count by any one’s standards.

My colleague is trying to convince the farmer to do another WormTest soon rather than drench.

So, let’s say it would cost say 50c (drench + labour) to drench the weaners. That’s $2500 worth. The farmer has not done drench resistance testing in recent years, so he/she doesn’t even know if the drench would have worked.

A WormTest with culture costs around $75. Let’s say four were done: that’s $300. That’s a whole lot less than $2500.

What if WormTesting indicated drenching was necessary. Say drench costs 25c per sheep, that’s $1250 worth of drench for 5000 animals. A ‘quick and dirty’ test (DrenchCheckDay10) to see if the drench was effective would cost two WormTests, one on the day of drenching , or within several days before, plus another 10-14 days after drenching. Say, $150 worth, if cultures were done as well. Again that seems more like an investment than a cost.

Subscribe to WormBoss: http://www.wormboss.com.au/

Some non-worm items that may be of interest:

* Healthcare’s trick coin

http://www.nytimes.com/2013/02/02/opinion/health-cares-trick-coin.html?hpw&_r=1& Article by Dr Ben Goodacre

* Machu Picchu – 16 Gigapixels http://skift.com/2012/11/15/this-may-be-the-best-photograph-of-machu-picchu-ever-posted-on-the-internet/

* Indirect Tracking of Drop Bears Using GNSS Technology. Volker Janssen. Australian Geographer .Volume 43, Issue 4, 2012 pages 445-452 http://ecite.utas.edu.au/82194