WA WormBoss Worm Control Programs
WA WormBoss Drench Decision Guides
Recommendations for all of WA:
Worm control advice for sheep last month was all about the likely risk of early worm development after rainfall in February. Since then, there’s been considerably more rain across much of the state in early March, and many districts have turned green.
The rapid growth of pasture and weeds will provide more than enough moisture to support a significant level of worm development. Spells of hot weather will reduce worm egg hatching and the survival of the larvae, but this will be temporary at best. Unless you’ve largely missed out on the rains, it’s time for action to keep pasture worm contamination as low as possible.
Worm control action
The key message is that worm counts should be as low as possible by the end of March at the latest.
As recommended last month, this means:
Mobs carrying over about 100 eggs per gram (epg) on average should be drenched. This is well below figures associated with production loss or signs of worms, but the aim here is to prevent further pasture contamination with worm eggs and larvae. The higher the worm count in autumn, the larger the worm burdens in winter and beyond.
Barber’s pole worm
As also noted last month, in areas prone to barber’s pole worm, the risk of problems will be considerably higher if there is a heavy mat of green pasture at this time of year. Unlike most other major sheep (and goat, and camelid) worms, barber’s pole needs warm weather, but it is especially sensitive to the need for moisture.
Even in the major barber’s pole worm zones in WA, it’s development is usually limited by the hot and dry conditions of early autumn, so we don’t often see large outbreaks with sheep deaths at this time. This year could be different! Wherever perennial pastures are kicking, barber’s pole worm will be ready to take advantage of the window of favourable conditions before cooler weather intervenes some months away. The risk in areas on the fringe of the usual barber’s pole zones will also be higher, and an absence in recent years may be about to change.
More frequent checks of WECs than usual will be good insurance against barber’s pole worm problems, as deaths due to rapid blood loss typically occur without obvious earlier signs in the sheep, despite the anaemia building over a few weeks, but regular worm egg counts will identify impending problems.
In all agricultural areas of WA, we can expect a higher risk of worm problems this year, unless managed effectively early in the season – and with continued monitoring as condition continue to favour worms over the next few months
Recently we have done a number of worm egg counts. In the majority of cases counts have been over 100 eggs per gram (epg). At this time of year an average count of this level warrants drenching. Drenching will reduce the egg output and ultimately the number of larvae that will survive to become the winter worm population. Recent rains in most parts of the district will ensure that soil moisture is adequate for pasture to grow, eggs to hatch and larvae to survive.
Warm, humid weather with intermittent rain provides perfect conditions for Haemonchus (barber’s pole). Unlike scour worms barber’s pole causes lethargy, pale gums, bottle jaw (swelling under the jaw) a tail in the mob when moving sheep, collapse of severely affected sheep and death.
Barber’s pole worms live in the stomach of the sheep. These worms attach to the stomach wall and suck blood which gives them a red and white “barber’s pole” appearance. The subsequent blood loss over a few weeks eventually causes the clinical signs described above, with deaths appearing to be sudden, but the course of the disease really takes some weeks. The "bottle jaw" is as a result of protein loss.
Larvae are ingested while grazing. These larvae develop into adult worms in the stomach. These worms lay eggs which are excreted in the faeces onto the pasture. When conditions are right the eggs hatch into larvae and the cycle starts again. In very hot dry conditions lasting several months eggs can be killed and will not hatch. If conditions are right for hatching but then we get some hot weather, larvae may die before being ingested by the sheep.
Conditions that favour pasture growth favour barber’s pole. It is important to be vigilant for signs of Haemonchosis (barber’s pole infection) at these times.