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Western Australia worms, flies and lice update - May 2018

WA WormBoss Worm Control Programs

WA WormBoss Drench Decision Guides





Albany: Brown Besier, Brown Besier Parasitology (

Like sheep, worms need rain to thrive. The absence of green pasture across most of the state for all of autumn will result in limited worm egg development, and sheep won’t have taken in large numbers of worm larvae so far. Depending on the weather pattern in the next few weeks, we may have a relatively light worm year.

Hopefully the rains expected to start in late May will kick off the growing season, but it will still be some time before there is a good pasture cover. 

The worm risk never totally goes away for several reasons:

- Worms are opportunists, waiting for suitable pasture conditions. Unless worm egg counts are very low in all sheep, worm numbers will increase within a few weeks of decent rainfall. The more worms that have survived in sheep – likely where drenches in summer and autumn were not fully-effective due to drench resistance – the larger the chance of significant problems later in winter.

- Sheep body condition may be lower than optimal, depending on the grain feeding program. Individual sheep below about condition score 2 are relatively susceptible to the effects of worms, and keeping ewe mobs at the condition levels recommended by LifeTime Ewe guidelines (average close to Score 3 at lambing) will generally ensure that they tolerate low to moderate worm burdens.

- Short pastures mean that sheep are grazing close to the ground, where most worm larvae are found. If there is even a small amount of green growth, the worm cycle will keep ticking along, as sheep chase the green pick.

For all these reasons, it is important to monitor worm burdens as we move into winter, and the worm potential increases. In areas with perennial pastures or unusually heavy rains, the risk will be higher, and on some properties significant worm egg counts may have already developed.


If drenched in autumn (as recommended), counts will be low and no pre-lambing drench should be needed for mobs due to lamb in May, and perhaps even June. A worm egg count check is wise if either lambing later than early June, or there is some doubt over the effectiveness of the most recent drench.

If ewes were given summer drenches, ideally with a small proportion left undrenched(for drench resistance management), it is close to impossible to predict pre-lambing worm burdens. Chances are that these will be low, especially this year, but for late-lambers at least, maybe not.

We recommend pre-lamb drenches at a mob average of 100 eggs per gram or over, a very low figure. This is to prevent heavy paddock worm contamination, and to reduce the worm risk to the lambs. Many ewe mobs will have worm egg counts at this level or more, but it won’t be visible to the eye – hence the advice to check egg counts.


By early winter, worm egg counts should be done every 4-5 weeks, at least on some representative mobs of this age group, and especially where body condition scores are lighter than ideal.

If scouring occurs at a mob level in this age group, it will almost always be due to worms – this can be confirmed by a worm egg count, but in most cases a drench is necessary. If there is little response to a drench, a worm egg count should be taken, and further advice sought.

Barbers Pole worm and blowflies

The late warm conditions will bring the potential for both barber’s pole worm and blowfly strike in the higher rainfall zones, although whether it actually occurs will depend on the amount of recent rainfall.

For barber’s pole worm, the risk could last for some weeks, provided there’s enough green pasture growth, with a particular risk in ewes about to lamb. The temporary loss of worm immunity during lactation allows worm burdens to increase, and for sheep with barber’s pole worm burdens the consequences can be lethal. In known barber’s pole worm areas, a worm egg count check on a few mobs is a wise precaution, especially if decent rains occur before about mid-June.

Hopefully there’ll have been better news on the rainfall front by the time of the next ParaBoss newsletter!


Esperance: Nicole Swan, Swan’s Veterinary Services (

Many properties are currently short on feed. This increases the risk of a worm problem for two reasons. Firstly, sheep will be grazing the pasture hard and therefore more likely to ingest worm larvae if they are present. Secondly, unless there is supplementary feeding they will be under some degree of nutritional stress which will reduce their ability to cope with a worm burden. Sheep that are in good body condition can cope with a low level of worms compared to sheep in poor condition. It is important to be regularly assessing the body condition of each mob and feeding them accordingly. This is especially important for pregnant and lactating ewes.

Farmers whose flocks lambed in autumn, should be starting to think about marking. Prior to marking, ewes should be monitored to see if drenching is required. Lambs should not need drenching as they will not have been grazing for very long. If there is good worm control in the ewes, then the egg output onto the pasture and potential for lambs to pick up worms will be reduced. The potential for larval pickup will also depend on the preparation of the lambing paddock. Once the pasture is green, larvae present will survive and be available for lambs to ingest. The best strategy is to have a lambing paddock set aside that has been cropped or not had sheep for 6 months (a clean paddock). Ewes are then monitored pre-lambing and drenched if required. On a paddock that is green and not clean, the majority of the worm population will be outside, not inside the sheep, and so unaffected by drenching.

At lambing the ewes’ natural immunity to any worms present in their gut is reduced. This is especially the case with barber’s pole (Haemonchus). If there are adult worms present in the ewes, then at and around lambing we often see a significant rise in the egg output of these worms. This rise can be very rapid. If you are in a barber’s pole area it is important to be very vigilant at this time. A pre-lambing drench that gives residual protection for barber’s pole is often good insurance against an outbreak. Barber’s pole does not cause scouring like other worms. The worm sucks blood and so causes anaemia (paleness), lethargy, bottle-jaw (a swelling under the jaw due to low blood protein), a tail in the mob when moved, and sudden death.

Discussing a drenching strategy with your local veterinarian is recommended.

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