Western Australia worms, flies and lice update - April 2017

Albany: Brown Besier, Brown Besier Parasitology (brown@bbpara.com.au)

WA state report

The past month may have been dry across most of the state, but don’t be fooled if pastures have dried off. The early rains in most of the agriculture areas have started the annual worm cycle and sheep will generally be carrying higher worm burdens than in more normal years with dry summers.

Despite some fairly hot days, a large percentage of worm larvae that developed after an early green flush will mostly have survived, and sheep will be picking these up as they graze. Where green feed has persisted or increased, the worm risk will be closer to the situation of a normal May.


The main aim should be to keep worm burdens at levels that do not cause significant production loss. It is now too late to prevent pasture contamination with worm eggs, so the tolerance of worm egg counts is somewhat higher than recommended for pre-emptive drench levels earlier in the year.

A proportion of sheep usually scour once there is a significant amount of green feed, driven by their first intake of worm larvae and the higher pasture moisture content. This has occurred earlier than usual in many areas, but it is important to understand the reason. If this is simply the “normal” process, where scouring indicates the development of immunity to worms, worm egg counts will be low and body condition won’t be significantly affected. If high worm burdens are present, this will be shown by relatively high worm egg counts, and their production performance will suffer.

Lambs/hoggets: Worm egg counts should be checked about every 4–6 weeks. A drench is usually recommended if average counts are over about 250 eggs per gram, or less if in poor body condition.

These sheep should have received an effective summer drench, so if counts are high (over 300 eggs per gram), it is likely that the drench was not fully effective. If so, it is recommended to check drench effectiveness—easily done by taking worm egg counts before and 14 days after the next drench is given (to sheep of any age). Ideally, full drench resistance tests will be conducted on lambs in spring.

Ewes: If due to lamb soon, or by the end of May, the question is whether a pre-lamb drench is needed.  If a drench was given (as recommended) earlier in autumn, or in summer, counts are likely to be low and no pre-lamb drench is needed. However, a worm egg count will be worthwhile, as counts may be higher (especially if the last drench was not fully-effective).

If a pre-lamb drench is needed, it should be given about 2 weeks before lambing is due to start.

Barber’s pole worm: This is likely to rear its heads in areas where it is normally only an occasional threat, and to be more of a problem in areas where outbreaks often occur. This is due to the favourable conditions last year, which mean sheep will often be carrying higher numbers of barber’s pole than usual. Where there was early pasture growth this year, the likelihood of problems will be increased.

The way to check whether there is a risk or not is to take worm egg counts. Barber’s pole worm typically has far higher counts than other worms, and this often helps indicate whether it is present in significant numbers. However, high but not enormous counts are harder to interpret, and talking to a veterinarian or advisor will help sort it out.

The result will indicate whether a normal broad-spectrum (all worm species) drench is needed, or treatment specifically against barber’s pole worm, such as the drench group, closantel. A single treatment usually removes the threat, and this will reduce as weather conditions become cooler.

However, in areas where there have been past problems with barber’s pole, or counts in ewes are especially high now, a pre-lamb drench to ewes with closantel may be wise. Other long-acting drench products are available and will also be effective, but they can increase the level of drench resistance. Their use should be discussed with an adviser, and are best used where justified by the worm pressure or past experience of worm problems.