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Long wool lice treatments—when are they justified?

By Deb Maxwell, ParaBoss Operations Manager
N
ovember 2014

If lice have been introduced to your previously lice-free flock, should you immediately treat, or simply wait until next shearing?

The Long Wool Tool at LiceBoss.com.au provides a simple way to help you answer this question.

The important factors that first must influence your decision are

  • How many mobs (and the proportion of the flock) have become infested with lice?
  • Aside from wool value, how will lice impact the flock?
  • A long-wool treatment will NOT eradicate lice; this can only be done with an off-shears/short wool treatment.
  • What is the cost in wool damage compared to the cost of applying a long wool treatment?

Weighing up your options

If you are certain few mobs have become infested, consider shearing them and applying an off-shears/short wool treatment to eradicate lice before they spread to other mobs within the flock. But weigh up how much you save by not treating your entire flock against treatment costs plus the cost incurred from premature shearing of the affected mobs.

While lice only affect the wool, not the animal’s weight, they can certainly affect your reputation. If you have a stud flock, for instance, you may decide that immediate shearing and off-shears/short wool treatment is the best way to protect your reputation.

Applying a long wool treatment will stop most further wool damage from occurring, but it does not eradicate lice. Therefore, an off-shears/short wool treatment will still be needed next shearing, and without effective isolation, lice can still spread to other mobs or neighbouring properties with straying sheep.

LiceBoss Long Wool Tool

There are times when a long wool treatment is a good option to limit further damage to the wool.

The LiceBoss Long Wool Tool is a very simple way to calculate and compare the cost of wool value loss, if no treatment is applied, to the approximate cost of a long wool treatment including chemical, labour and current wool value loss.

LiceBoss is Australia’s lice control resource, providing practical information on prevention, monitoring, treatment, products, and decision support tools.

The following example using the LiceBoss Long Wool Tool shows where lice have been found in a mob of 1000 ewes with 1% showing rubbing and an average lice-free fleece value of $40. Figure 1 shows the inputs into the Long Wool Tool, which are simply month of last and next shearing, the month when you see sheep rubbing, the likely value of fleeces at next shearing and the number or % of the mob seen rubbing.

The resulting report (Figure 2) allows you to compare the cost of lost wool value to the cost of treating the sheep in long wool. 


 Figure 1. Extremely simple inputs are used to assess the costs of no treatment versus a long wool treatment in a lousy mob.
Figure 1. Extremely simple inputs are used to assess the costs of no treatment versus a long wool treatment in a lousy mob.

Figure 2. The Long Wool Tool report shows costs of various long wool treatment options against the cost of wool damage.
Figure 2. The Long Wool Tool report shows costs of various long wool treatment options against the cost of wool damage.

A key input to the tool is the time when rubbing is seen in relation to the previous and next shearing. This reflects when the sheep have become infested; rubbing is not generally noticed until a few months after lice have been introduced.

Varying the time when 1% of the sheep were seen to be rubbing shows how the decision to apply a long-wool treatment changes in regard to the time from and to shearing. In Table 1, the month when 1% of the mob is seen to be rubbing (in relation to next shearing) is varied. The costs for each scenario reported by the Long Wool Tool are shown in the right hand columns.

Table 1. Results from the LiceBoss Long Wool Tool showing scenarios with a mob of 1000 ewes, with an average (lice-free) fleece value of $40, when 1% of the mob are first seen rubbing at 10, 8, 6, 4 and 2 months before shearing.

Months until next shearing when 1% of the mob are seen rubbing

Cost of wool loss if no long wool treatment is applied

Approximate cost of various long wool treatment options including chemical, labour and current wool loss

IGR jetting

ML jetting

IGR backline

Spinosyn jetting

SP backline

Spinosyn backline

10

$9,500

$1,100

$1,700

$2,300

$3,800

$5,200

N/A

8

$5,700

$850

$1,100

$1,800

$1,900

$2,500

N/A

6

$2,400

$820

$1,000

$1,200

$1,600

$1,600

N/A

4

$670

N/A

$1,100

N/A

$1,200

$1,300

$2,100

2

$140

N/A

$1,200

N/A

$1,300

$1,200

$2,000

Note: The costs associated with a particular treatment vary because wool damage from lice still occurs despite long wool treatment, as the lice are not eradicated; only suppressed. As the effectiveness of the chemical  wears off and lice numbers increase again, so the amount of wool damage will increase—this extra amount is most obvious in the treatments given 10 months before shearing. Treatment in longer wool also requires additional chemical. 

Table 1 shows that when a small number of sheep are first seen rubbing when there are still many months until next shearing, then the eventual damage to the wool value will be much greater than when rubbing starts close to the next shearing. This is because the lice have a greater time to build up on individual animals and spread to more animals within the mob, so causing more damage.

In this scenario (where the average fleece value was predicted to be $40), it is cost-effective to apply a long wool treatment if 1% of this mob were seen to be rubbing more than 6 months before shearing, but when this was closer to next shearing the cost of damage does not outweigh the cost of treatment.

In summary, the LiceBoss Long Wool Tool is very simple to use and indicates whether it is cost-effective to apply a long wool treatment to lousy sheep.