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Western Australia worms, flies and lice update - March 2018

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

WA sheep worm outlook for April 2018

This is a key time of year for sheep worm control: by mid-April, worm egg counts should be close to zero for all classes of sheep (and goats, and camelids).

For most of the state, where summer rains didn’t result in much green pasture growth, and there have been some recent high temperatures, we have the prospect of very good worm control over the coming months.

However, where green pasture has developed and persisted, and sheep are likely to have been carrying any sort of worm burden in summer, there is a higher worm risk. It is especially important that sheep in this situation are drenched or worm-checked during April.

Ewes

As outlined in earlier newsletters, there are two ways to go with worm control in adult sheep over summer and autumn, as they are the key to effective drench resistance management. The aim is to keep some worms in them that have not been exposed to a drench since last winter or spring, as adult sheep in good body condition can tolerate a small worm burden.

If the ewes were given a summer drench a small percentage (10-20%) should have been left undrenched. Worm egg counts should now be done in a couple of representative mobs, and if averages are over 100 eggs per gram, drench all ewes. (Better, do this mob by mob – some may have lower counts and you can save a drench).

If the ewes were given a summer drench with all the mob drenched, counts should also be checked – if the drench was not 100% effective, some worms may be present. Many of these will be drench resistant, and if over about 100 eggs per gram, they need to be removed. (Next year, plan to leave some undrenched in summer.)

For ewes to be given an autumn drench (i.e., not in summer), plan this for between now and mid-April. By then, a small population of worms not recently exposed to drenches will be developing on the pasture, ready to dilute resistant worms left in other sheep classes (i.e., lambs and yearlings).

As a refinement, checking worm egg counts of each ewe mob may allow some drench saving, but if all or most are over 100 eggs per gram, this indicates that all ewes need this drench as a routine.

For ewes pre-lambing: If due to lamb soon (April or May), autumn-drenched ewes often need no extra treatment. Again, we want counts in late-pregnant ewes to be below 100 eggs per gram.

If lambing later, ewes often do have significant pre-lambing worm counts. A worm egg count (WormTest) taken three weeks out from lambing will give time for this treatment if needed.

Lambs

Check worm egg counts now, and if over 100 eggs per gram, drench. Their worm immunity will usually still be developing, and even a small burden now is likely to rapidly increase after the season’s break.

Worm counts should then 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.

Barber’s pole worm

This may rear its head where it is a common or occasional player, and where there was early pasture growth this year, the likelihood of problems will be increased.

Take worm egg counts to check the risk – barber’s pole worm typically has far higher counts than other worms. However, high but not enormous counts are harder to interpret, and talking to a veterinarian or advisor will help sort it out.

Bottom line: make sure that worm counts are very low by the end of April at the latest, so worm populations start the new worm year - after the season’s break – from a low base.

 

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

In the last few weeks we have done faecal worm egg counts from a number of properties. Mob averages have ranged from 0 eggs per gram (epg) to 110 epg with individual counts on one property as high as 700 epg. This property has a history of haemonchosis (barber’s pole worm infestations).

Now is a critical time to conduct faecal worm egg counts (WormTests). With the recent rains sheep should be monitored now to determine if an autumn drench is required. Sheep that did not receive a drench earlier in the summer will, more than likely require drenching. Sheep that were drenched should still be monitored as their worm burden will be influenced by where they have been grazing, their age, and in younger sheep, their natural immunity.

A drench at this time of year will reduce the contamination of winter pastures.

Depending on the time of lambing this drench may coincide with a pre-lambing drench. If ewes do not lamb until mid-May or later they will still require a drench now. If ewes are not drenched now, then lambs will be exposed to larvae deposited on the pasture between now and the pre-lambing drench.

It is important to use an effective drench for this autumn drench.