Western Australia worms, flies and lice update - June 2017

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

 

Across the state: the dry season experienced by most of the state is dominating farming sector conversations at present, and for most of the state, much more is needed than the dribble of rain at the end of June. Except in some coastal areas, where recent rains will have been useful, pasture growth has been very poor.

Unfortunately, dry conditions don’t give any benefit for the control of worms in sheep and other livestock, and can increase the need to be on top of the worm situation, for several reasons:

  • Poor pasture growth due to low rainfall does not mean that there is a lower worm risk, unless there is no pasture growth at all. Provided that some green pasture is present, enough moisture will come from dews and small amounts of rainfall to prevent dryness from killing worm eggs and the larval stages. Temperatures have favoured worms for many weeks, as only continued hot weather will have a major detrimental effect. (An exception is barber’s pole worm – unlike other worm species, cool conditions do inhibit their development.)
  • Body condition has a big influence on how well livestock cope with worms. The visible effects of worms on sheep (ill-thrift, weight loss) are more pronounced in sheep below about Score 2 than above Score 3. Keeping ewe mobs at the condition levels recommended by LifeTime Ewe guidelines will generally ensure that they tolerate low to moderate worm burdens, whereas ewes in poor condition will be affected, with knock-on effects to their lambs.
  • Short pastures mean that sheep are grazing in the zone where most worm larvae are found. After the larvae hatch from worm eggs, they move onto herbage, with the great majority within 5 cm or less of ground level. There is therefore none of the dilution effect seen where sheep graze higher and more dense pastures. 

Putting all this together, it is important to ensure that worm burdens stay within manageable limits through winter.

Ewes: if they are putting out large numbers of worm eggs, their lambs will be exposed to a heavier worm challenge than necessary, or ideal. A pre-lamb drench is recommended where average mob worm egg counts (WEC) are above about 100 eggs per gram (epg). This is a very low figure, and unless the ewes have remained on a crop stubble after a summer or autumn drench, chances are that counts will be higher and a drench warranted.

A worm egg count on a couple of mobs will quickly indicate what action is needed. Where ewes were not drenched or worm-counted pre-lambing, a count before lamb marking will be useful, as high counts may show that a treatment is needed then. (At this time of year, lamb and ewe faecal pellets can easily be distinguished by size.)

Ed: If lambs are still with their mothers, samples from the lambs must be collected and tested separately from the samples from their mothers.

Weaners/hoggets: counts should be done every 5-6 weeks if the general body condition appears worse than expected from the nutritional situation. If scouring commences, 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. However, if there is little response to a drench, a worm egg count should be conducted and further advice sought.

Barber’s pole worm: as noted, cool conditions slow development, but barber’s pole larvae already present on the pasture will survive for some weeks or months. A pre-lamb worm egg count is especially necessary in barber’s pole-prone areas, and if counts are high, specific treatment to suppress further larval intake may be warranted.

Let’s hope that there is enough rainfall in the next month to benefit pasture, crops and livestock, and ease the risk of worm problems.

 

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

We have done some pre-lambing counts this month. All counts have been reasonably low (60 eggs per gram (epg) or less average). These sheep were from a property that is at risk of barber’s pole. However, in recent years there have been few problems. On this property sheep are drenched with Closantal in October. The rationale for this is that sheep while grazing will consume barber’s pole larvae and in effect, vacuum up the worm larvae as the pastures start to dry off for summer. Any larvae consumed will not develop while the Closantal is active. Closantal gives protection for the sheep of 4 weeks and up to 7 weeks protection from recontamination of pastures*.

For these ewes it was recommended that Closantal was given pre-lambing to prevent any outbreaks over lambing. These worm egg counts showed that a broad-spectrum drench was not required as only barber’s pole was present.

While these ewes are due to lamb in 3 weeks, other clients are about to, or have just marked their lambs. Lamb marking is an opportunity to drench the ewes if required. You should check the worm status of the ewes by doing a worm egg count (WEC) on the mob prior to getting the ewes in the yards, then if required you can drench them when the lambs are marked. Lambs should not require drenching as they have not been grazing for a significant amount of time. However, if the risk of barber’s pole is high, especially if there have been clinical cases in the ewes, I would consider a closantal drench for the lambs to protect them until weaning. A closantal drench will not affect the results of any drench resistance testing (DrenchTest) that you may want to do with these lambs at weaning, as this testing is predominantly for scour worms.

Now is the time to speak to your veterinarian about drench resistance testing. This is conducted on undrenched weaners (They can have had Closantal but no other drenches). The number of drenches and which drenches you test will depend on your drench history and the results of previous tests.


*Ed: Closantel provides sustained action against mature and immature barber’s pole, and protects against reinfection from ingested larvae for 4 weeks after dosing. Any worm larvae picked up from the pastures after this time take 3 weeks to mature and release eggs back onto pasture.