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Western Australia worms, flies and lice update - January 2018

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

WA State parasite control outlook:  

Mid-summer is usually a dull time for parasites, as it’s generally too hot and dry for worms and blowflies. However, wherever some green feed survives there is some worm risk, and the heavy summer rains will put this on the radar in some districts.

If you’re shearing in late summer or autumn, lice treatments are an issue—more on this below.

Worms—where we should be?

Weaners and hoggets (white and black tags) should now have the lowest worm burdens of their lives. In most districts, they should have had a drench within the last few weeks, either before being moved onto crop stubbles, or after the feed has dried off, if staying in a pasture paddock.

If no drench has been given within the last 2 months, or you are not certain it will have been fully effective (due to drench resistance), worm egg counts (WormTest) should be checked. If counts in these sheep are more than an average of 50 eggs per gram, a drench is usually warranted. Carrying worms into autumn is typically the start of worm problems in winter and spring.

Adult sheep: It’s a bit different for these, as we want them to carry a small number of worms that have not recently been exposed to a drench, to seed autumn pastures with a less-resistant worm population. This is a key part of farm-wide drench resistance management strategies, aiming to dilute resistant worms that may have survived in younger sheep.

So, ewes and other adult sheep should have either had a summer drench (such as onto crop stubbles) but with 10% or more left undrenched, or they should be waiting on a drench in autumn.

If any ewe mobs are in poorer condition than ideal for this time of year, a worm egg count will show whether worms are holding them back. Where average body condition scores are around 3.0 or more, worms are rarely an issue, but if closer to score 2.0, worms could be having an effect.

Have the January rains made a difference?

Summer rains are a mixed blessing, and there’s bound to be some green appearing in some districts. Whether it affects worm control depends on whether a dense mat of green pasture develops, and whether it lasts for more than a week or two. Both these situations are necessary for there to be much of a worm risk.

Even if there is little germination or it dies back fairly quickly, some green feed may persist along creek lines, providing a refuge for worms for some time. Whether this is of consequence for worms depends on whether the sheep in a particular paddock carried many worms at the time. For example, if they were drenched onto a crop stubble, some green growth will have no effect on worms.

However, where perennial pastures have greened up, or there is a question about how wormy the sheep were at the time (including ewes waiting to be drenched in autumn), it will pay to check worm egg counts. This is best done a month after the green feed appeared, and if average counts are over about 50 eggs per grams (young sheep), or 100 eggs per gram (ewes), a drench to the whole mob is recommended. If less than this, no change from the usual program is needed.

Barber’s pole worm a risk?

Last year, summer rains led to a flurry of barber’s pole worm outbreaks and sheep losses in some districts. The same risk will apply this year, depending on the amount and duration of summer rain. A few worm egg counts (WormTest) are always good insurance in barber’s pole worm areas after out-of-season rain.

Lice treatments

Shearing will be on the agenda for many graziers in the next few months for at least part of the flock. Before purchasing chemical for an annual treatment, it’s worth considering a few points.

  • Is any treatment necessary? If you’ve seen no signs of lice infestation in the past year, no stray sheep have got in and boundary fences are good, the flock may well be lice-free. The products likely to be effective (no lice resistance) have little long-term action, so there’s little point in treating off-shears for protection against re-infestation.
  • Take a risk-assessment approach: The more neighbours you have and where fences are not up to scratch, and the more shearing times over the year, the greater the risk of lice introductions. However, if inspections on several mobs show no lice, full musters can be guaranteed, and the risk of infestations from neighbours is relatively low, it is probably not cost-effective to treat off shears as a routine. Obviously, swift action is needed if stray sheep appear or some mobs show signs of rubbing.
  • Make sure that chemical treatments do the job. Resistance by lice is common to the synthetic pyrethroid and insect growth regulator products, but there are several off-shears chemical groups that can eradiate lice. No long-wool products are registered for compete lice removal, so where these were used a further treatment at shearing is still advised. 
  • Correct chemical application is essential, and all product instructions have details on how to get the best result. Dipping can be highly effective, but it is essential that the sheep are wetted to the skin.

The LiceBoss website has chapter and verse on factors affecting the lice risk and treatment decisions: see www.liceboss.com.au, or for information on all sheep parasites and goat worms: www.paraboss.com.au

 

Esperance: Nicole Swan, Swan’s Veterinary Services (nicole@swansvet.com)

Along with the Christmas and New Year break so has come warmer weather. Despite this we have recently seen evidence of barber’s pole causing high faecal worm egg counts (WormTest) in weaners.

Weaners tested today were drenched 1 month ago with a triple-active abamectin/oxfendazole/levamisole mixture onto pasture as no stubbles were available. Recently, a couple of sheep have died. Counts conducted today on 2 mobs had an average of 715 eggs per gram (epg) and 1130 epg with counts ranging from 150–4650 epg. There is no scouring in these mobs.

Due to the high faecal worm egg counts in these sheep they are being drenched prior to any further workup to confirm barber’s pole. Drenching with a broad-spectrum drench as well as a drench that will give prolonged action against barber’s pole has been recommended. The original plan was to sell these sheep in 4-5 weeks as fat lambs. Withholding periods for any drench used will need to be observed. Given the time frames and a withhold of only 7 days, drenching with Cydectin (moxidectin) has been recommended. If these sheep are not sold as planned then a follow up worm egg count in 6-7 weeks post drenching is recommended.

Cydectin has a residual effect against barber’s pole though not as long as Closantel. However given the time frames its duration of action should be adequate in this situation.

The cause of the high counts could be drench resistance to the triple-active and/or extreme contamination of the pastures has allowed enough re-infection to cause clinical signs within the month. A follow up WormTest (DrenchCheck) is planned on these lambs at 14 days and again at 28 days after the moxidectin drench to check for drench resistance considering it is a macrocyclic lactone (ML) and the original drench had an ML (abamectin), albeit a less potent one than moxidectin.

A full drench resistance test (DrenchTest) is highly recommended for this, and in fact, all sheep properties, preferably testing the single actives, which gives a better picture of overall drench resistance and can be used to calculate resistance to combinations.