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Western Australia worms, flies and lice update - June 2014

Perth region and Central Wheatbelt: Ray Batey, Sheepvet Australia (ray@sheepvet.com.au)

Building a worm control strategy based on advice

In early June, a grazier client asked me to advise what he should be doing about worm parasites—not in the present, but for when he weans lambs in late August.

The next 4–5 months coincide with the principal period of contamination by and pickup of worm larvae in this area. Thus, early winter is the critical time of year to develop or review a worm control strategy—taking account of recent treatments, times of lambing and weaning, pasture growth, and current or anticipated body condition of both ewes and hoggets. Such an approach enables more rational and cost-effective use of both chemical and non-chemical methods of worm control.

My client’s request for advice almost 3 months in advance enabled a consideration of the options available to his enterprise. Our conversation included evaluating how the season has progressed and the likely impact of previous treatment of ewes. A simple risk assessment suggested that worms are unlikely to have any impact for this enterprise in the medium term, and that the ewes will probably not need treatment at weaning. Despite a high level of resistance to most drench chemicals on this farm, there has been minimal impact because he has that knowledge and is able to plan treatments accordingly, including, on this occasion, deciding which chemical to use on the weaned lambs. We also agreed on undertaking a limited test of resistance, confined to those chemicals he will use.

This forward-looking and targeted approach will be more cost-effective and involve less risk than control measures adopted by many farmers, which rely solely on treatments at particular times irrespective of what is happening in worm populations.

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

This week we have had more rain. But now that it is colder the pasture growth is slow. A lot of farmers are still supplementing sheep especially lambing ewes and this is likely to continue for a while. Farmers in the coastal barber’s pole areas are reminded to remain vigilant.
Average counts from 8 ewe mobs on a property in Ravensthorpe varied from 80 epg to 285 epg. These mobs had not been drenched since April/May 2013. Lectin test results came back that there was no barber’s pole present. Counts in individual sheep ranged from 0 epg to 1800 epg. This highlights the effectiveness of a drench on this property at this time of year. These ewes have made it through 12 months without any clinical signs of worms. Last year was a very good feed year and that would have reduced the feed pressure and therefore the likelihood of a low to moderate worm burden having any clinical impact. This is the first time Drench Resistance Tests have been done on this farm by our practice so no previous data is available. A drench for ewe mobs early April each year will be recommended on this property.
Weaners on the same property were drenched in October 2013 with moxidectin. The ewe weaners had a count of 5 epg. The wether weaners were 130 epg. Some of these were scouring.

It is recommended that ewes are monitored at lamb marking time to determine if drenching is required.

Albany: Brown Besier, DAFWA (brown.besier@agric.wa.gov.au)

WA overview report, June 2014

Worm burdens will generally still be low where summer and autumn drenches were effective, but will be increasing now that there has been green pasture growth for some weeks.

The main actions recommended:

  • Check worm egg counts in hoggets (2013-drop) sometime in the next 4 weeks, and earlier if there are signs of worms (scouring, poor growth). Where it is possible that drenches were not as effective as needed, due to drench resistance, worm burdens will be more advanced and monitoring is more urgent.
  • Check worm egg counts in ewes due to lamb within the next 2–3 weeks. In many cases, counts will still be low if an autumn drench was given, but a drench should be given if counts are over about 100 eggs per gram, and certainly at a maximum of 200. This should be with a broad-spectrum drench, but in barber’s pole worm-risk areas, a closantel (narrow-spectrum, long-acting) drench may be needed if counts are high enough.

The main aim of pre-lamb drenching is to reduce the level of worm contamination of the pasture so the lambs are not exposed to heavy worm larval intake as they grow. It is especially important that ewes don’t carry significant burdens at this time, as their worm egg output increases considerably during lactation—this is only temporary and they will regain their worm immunity, and counts will decline to lower levels after about 2 months. However, pre-lamb treatments should be avoided if a summer drench was given to the ewes, as they add a lot of pressure for drench resistance.

Lambs coming up to marking: there is rarely any value in drenching on the marking cradle, as the lambs have not taken in sufficient worm larvae to have significant burdens. However, plans should be in place for their worm treatments, usually their first drench at weaning, or between 12 and 16 weeks if not weaned by then. Ideally, the lambs will go onto pastures managed to have good nutrition and a low worm level, as they will be at their most worm-prone at that time.