Drench resistance monitoring program – Autumn 2023

Riverina Local Land Services is working with farmers to run a drench resistance monitoring program to help you understand the efficacy of the drenches you use on farm for worm control in sheep and cattle.

With breaking rains during a drier autumn stimulating sudden worm burden activity, take this chance to check your drench efficacy.

About the Riverina Local Land Services drench resistance monitoring program

The drench resistance monitoring program gives you the opportunity to test for worms in up to two mobs of stocks (i.e. ewes and weaner lambs or cows and weaner calves) with a WormTest Gold Kit.

A test is done before drenching to give a faecal egg count and larval identification.

This first monitoring is followed up 10-14 days later on the same stock with another WormTest Gold Kit to measure the drench efficacy or resistance to that type of drench group used.

What’s on offer and availability

We are working with the NSW Department of Primary Industries (DPI) Parasitology and Laboratory Testing to provide WormTest Gold Kits.

Through this program you can buy two WormTest Gold kits and get two bonus WormTest Gold kits.

The WormTest Gold Kit costs $96.34 each and landholders can buy two (total $192.68) and receive a bonus two for the follow up worm test carried out 10-14 days after drenching the livestock.

This opportunity (up to four kits) is limited to the first 50 landholder participants with livestock.

WormTest Gold Kits are available for collection from Wagga Wagga, Temora and Hay Local Land Services Offices.

For other areas in the Riverina, please contact Martin Preuss, Land Services Officer (Livestock) on 0455 729 318 or email martin.preuss@lls.nsw.gov.au for availability.

Is worm burden and drench resistance monitoring required during drier periods?

Generally, more frequent drenching is required during higher rainfall periods. This, combined with occasional under-dosing and drenching when there are higher worms on pastures, produces greater selection for resistance in worm populations.

However further research has shown that drench resistance can also develop during period of lower rainfall across the pastoral areas of Central, Riverina and Western NSW.

Field works several years ago in the Deniliquin and Corowa areas indicated that 30 per cent of flocks across 17 farms investigated had ivermectin-resistant Teladorsagia (Ostertagia) circumcincta (Ref. #1).

The problem with Nematodirus

Nematodirus (a thin-necked intestinal worm) is usually not a big problem in sheep, but under certain conditions it can be!

This parasite's little speciality is its hardy egg. It can survive a long time on pasture under tough, droughty conditions. Then, with a break in the season and good rain, younger sheep can pick up sizeable burdens of Nematodirus in a short time.

The result may be scours and ill-thrift, sometimes with low or even zero Nematodirus faecal egg counts.

A study conducted in 2005 across the South-West Slopes of NSW, found the region had Nematodirus problems two years running in Autumn drop lambs.

In one case, lambs were drenched with a known effective drench at marking, and three weeks later had a clinical problem with Nematodirus.

The researcher proposed that the reasons for this may be the weather pattern across the South-West Slopes and other similar NSW districts during the two years 2004 – 2005). This saw a very dry autumn, and a season break occurring a month or so later (around May/June) than usual (Ref. #2).

Concerns with Nematodirus burdeb

After a dry late summer and early autumn across Southern NSW during 2023, this worm burden situation could develop again this year with a good autumn break over the next few months.

The solution

Regular worm testing (worm egg count monitoring) with a WormTest kit is one of the best practices of good worm control.

A drench resistance check is done with a second WormTest check 7-10 days after the first drench.

This is a quick measure of drench efficacy.

References

• #1. Salmon D (2005). Riverina sheep worms, including ML resistance. Turning the Worm newsletter, Issue 19, December 2005. ISSN 1442-8466.
• #2. Evers J (2005). Nematodirus – A Conversation. Turning the Worm newsletter, Issue 19, December 2005. ISSN 1442-8466.
• DPI - Drench resistance and sheep worm control
• WormBoss - Drench decision guide