WA WormBoss Worm Control Programs
WA WormBoss Drench Decision Guides
Lambing will be over on the vast majority of sheep properties in WA, so the main worm control focus is on the lambs. As many farmers have found, it’s a pretty wormy year, driven by the early pasture growth that gave worms a longer time than usual to build up.
Pastures across the state must be considered wormy now until it starts to dry off, unless a paddock has been spelled from wormy sheep for 3–4 months. This is possible if cattle have grazed a particular paddock, or sheep were drenched before they went into it. But in most cases, green pasture means there is sufficient moisture to support worm egg development, and cold weather will have little adverse effect on this, other than for barber’s pole worm.
Whether or not worm problems occur over the next few months depends mostly on how well worms were controlled back in autumn, and that’s very hard to gauge. The main aim now is to stay on top of worms by monitoring with worm egg counts, and making sure worm-susceptible sheep (especially lambs) are not moved into wormy paddocks.
Lambs at marking: In general, lambs shouldn’t need a drench until about 12 or more weeks of age, unless worm control in the ewes was poor and the pastures are knee-deep in worm larvae. If the ewes had a drench before lambing, their lambs are unlikely to have significant worm burdens at marking-time.
Lambs at 12–14 weeks: By this time, lambs have generally had sufficient grazing time to take in significant numbers of worm larvae, if the paddock was wormy. This is usually hard to determine, and hence a routine weaning drench at this age is recommended. However, if weaning occurs when the oldest lambs are more than about 16 weeks, worm burdens are often significant, and either signs of worms (scouring) are seen, or growth rates may be reduced. In this case, a worm egg count will indicate whether a drench would be useful, and a decision can be made on whether weaning should be brought forward, or a drench given while lambs are still with the ewes. Growth rate penalties are obviously especially costly in prime lambs.
Hoggets (last year’s lambs): If more than, say, 10–15% are scouring, give a drench to all. It’s almost certainly due to worms, and scouring indicates that their immunity is developing. Chances are that most hoggets in good condition will handle worms for the rest of the season without much further scouring. However, they should be checked every 6 weeks or less to see whether low-level burdens may be affecting production.
Ewes: Visually check ewes for signs of worms, and if significant scouring is present, take a worm egg count. If counts warrant treatment, it may be feasible to drench at lamb marking. Once the lambs are 8–10 weeks old, ewes recover their worm immunity (temporarily depressed over lactation) and worm burdens begin to reduce from then on.
Barber’s pole worm: Although mostly confined to districts where some green pasture persists over summer, we saw more cases in May–June, and even early July, than in recent years. This was driven by the early green pasture conditions, which allowed numbers to build up earlier than usual. The cold weather will quickly suppress its development, and the only risk left now is in lambing ewes if their paddocks have large numbers of barber’s pole larvae left from early winter egg development. However, it will rear its head again in late spring, when lambs will be at particular risk.
Cold and consistently wet weather means that winter is truly upon us.
Recent worm egg counts have been varied and ranged from averages of 10 eggs per gram (epg) to 2,220 epg, with some individual counts as high as 11,350 epg.
The eggs in the latter counts were identified as Haemonchus (barber’s pole). Affected sheep on this farm were drenched with closantal in May, and as closantal has a residual affect for 7 weeks (i.e. a protection period of 4 weeks plus a further 3 weeks or so before eggs will again start to contaminate the paddock), these counts indicate that, on this farm, there is ongoing and severe worm contamination of pastures.
Drenching was recommended for this farm. A long-acting moxidectin injectable, or capsules may be a better management solution in this case to protect sheep. At this time of year, selection for drench resistance is minimal as the majority of the worms are on the pasture, compared to numbers in sheep. Diligent monitoring following drenching, was also recommended.