Mid-springtime brings two main sheep worm considerations: drenches for this year’s lambs (mostly at weaning), and drench resistance tests. It also brings blowflies!—earlier than most years for many districts.
A drench is recommended for most situations when lambs reach between 12 and 16 weeks of age, as lambs are then at their most worm-susceptible time of life.
Lambs to be weaned: Drenching should be done as a routine operation—there is usually little point in doing a worm egg count as counts almost always justify a drench. The main exception is where lambing was on pastures planned to be worm-free (ewes drenched into a clean pasture, or given slow-release capsules)—in this case a worm egg count will indicate the need.
Lambs not to be weaned at this time: Many prime lambs are not weaned until the first draft is sent off—but worms are also likely to be present and can reduce lamb growth rates. A worm egg count is recommended to check whether drenching can be delayed until lambs are yarded for drafting, or treatment is needed before then.
We don’t often see worms as a real problem in lambs less than about 12 weeks of age, and usually not until a few weeks later than that. However, wormy situations occasionally develop earlier, especially where ewes have carried high worm burdens into lambing paddocks. If drenching of lambs is needed earlier than about 14 weeks of age, a review of the worm control program is needed for future years.
Drench resistance testing kit
It’s also time to think about drench resistance testing—weaning is the best time from both the convenience and worm burden viewpoints. The resistance picture has moved on in recent years, and you can no longer assume that commonly-used drenches will still be effective. Resistance to moxidectin now affects about 30% of WA sheep properties.
DAFWA has a pre-paid kit which contains the hardware needed: a small amount of 4 different drenches, sampling equipment, pre-addressed postage bags and clear instructions. A comprehensive report is provided on the drench test results, with recommendations for the best options for various situations.
The cost is $440—mostly to cover the laboratory work. The cost is easily returned by ensuring fully-effective worm control by using the best drench option.
Obtaining the kits: visit or phone a DAFWA office to talk through the test requirements, organise pick-up or despatch of the kits, and arrange payment. As well as local DAFWA offices, the default is the Albany office (9892 8444).
There have been many reports of flystrike earlier than usual, presumably as a result of early warm weather. Recent heavy rains will keep the problem going for some time yet, where temperatures remain mild.
Most farmers have weaned their lambs by now. Unless information from recent Drench Resistance Tests has been available I have recommended that farmers use Zolvix or a triple combination (abamectin or Cydectin plus a white and clear) for their weaning drench.
Lambs and hoggets should receive a summer drench onto stubbles. Ewes and older wethers should be monitored to determine whether a summer drench is required. Sheep with counts of 200 epg or more should be drenched.
It is important that if all mobs require drenching that some sheep are left undrenched to ensure refugia occurs. It is important that you do not select for a super-resistant worm population on the farm. By leaving some sheep undrenched, the worms left in these sheep will dilute the population of any resistant worms left behind in the drenched sheep.
Counts done this month on ewes and lambs have been relatively low (averages 20–80 epg). One mob of lambs had a significant number of nematodirus. With the recent rain event (some areas had over 100 mm) and the warm weather, farmers will need to watch out for barber’s pole worm outbreaks.