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Introduced sheep—should I treat them?

by  Lewis Kahn, Executive Officer, ParaBoss

28 April 2015

I was recently approached to weigh up the lice control options for 1000 lousy near-full woolled sheep that were to be purchased and brought home to an existing flock of 3000 (august shorn) sheep, with all sheep needing to be joined soon and limited ability to quarantine. What were the options?

The first consideration was the likely cost of wool damage in purchased and existing sheep if no treatment was applied and sheep were boxed together. This involved comparing the cost of treating 1000 sheep on introduction to the later treatment of both the existing 3000 plus the introduced 1000, plus associated fleece discounts.

Considering that the introduced sheep were close to 12 months wool with obvious lice and wool damage, not shearing was a poor option, as the introduced sheep needed to be boxed with the existing flock for joining that were lice-free and still 4 months from shearing.

This meant that the second consideration was how to rapidly remove the lice infestation so sheep could be mixed together quickly, as effective quarantine for so many sheep was going to be very hard, and the preference was to create joining groups from a mix of the new and existing sheep.

While a backline or spray-on product could be applied straight off-shears, the downside was the 4–6 week period before treated sheep could be mixed with the lice-free sheep. As joining would occur earlier than that, this left dipping as the only option because a dip product gets all over the body immediately and can start killing lice straight away. The existing shower dip on the property was no longer considered useful, as shower dips are known to have a poorer success rate in fully wetting sheep, which is needed for eradication. A plunge or cage dip was the solution and so local contractors were sought and engaged for what should be a one-off activity.

The sheep were shorn on arrival and were able to be quarantined for the 10 days before dipping.

The LiceBoss Products Tool was used to choose a suitable chemical treatment. While the synthetic pyrethroids and IGR groups were discounted due to the possibility of resistance, both the neonicotinoids or organophosphates were good choices. Once treated, the sheep were able to be mixed together into joining groups less than a week later.

All mobs will be thoroughly checked for lice prior to the main August shearing, to determine whether eradication was successful, though at only 4 months away it is possble that a very low lice population could exist unnoticed. The plan will be to bring the new sheep into line with shearing the following year, as the fleece discounts from a prem. shearing this time round would be too costly.

The complexity and variety of scenarios can make treatment decisions difficult. With this in mind, the ParaBoss team have recently developed a LiceBoss Treatment Guide, which allows a sheep producer to work through the key questions to come to the most appropriate treatment option for the circumstance.

I used the LiceBoss Treatment Guide to work through the scenario above, with the results agreeing with the recommendation from our LiceBoss expert and ParaBoss Technical Committee member, Dr Peter James.

The LiceBoss Treatment Guide is currently being programmed onto the LiceBoss web site as an easy-to-use decision-tree tool—a series of simple questions where you select an answer and are taken to the next question and finally to a recommendation. It is due for release in June 2015 at www.liceboss.com.au.

If you'd like to try out a similar tool, a set of regional Drench Decision Guides exist on the WormBoss web site.