A good biosecurity plan must assume that introduced sheep are infested with lice regardless of their history or whether there are no lice or signs of lice. A new lice infestation may take 3–6 months before sheep are seen rubbing or lice can be found. Your decision on how to manage the introduced sheep will be a personal risk management choice. This is based on:
• The number of sheep being introduced, how many this is in relation to the existing flock size, the cost of their treatment and impact of out-of-season shearing compared with the cost and impact of treating the whole flock if lice spread to them.
• Your ability to properly quarantine the introduced sheep both until they can be treated off-shears or in short wool and for a period afterwards, while the treatment takes effect. This will depend on the product used and application method; see the label for the recommended time, but it can be many weeks.
Management options for introduced sheep
There are four management options to keep your flock lice free in the long term. You can use the LiceBoss Treatment Guide to help choose an option to suit your situation.
The options are presented below in descending order of biosecurity rigour. Additional notes for the options are further below.
Option 1: Shear and treat immediately*
1. Shear regardless of when sheep were last shorn.
2. Apply an off-shears/short wool treatment.
3. Quarantine for the required period after treatment, as shown on the product label.
Note: This option may produce high chemical residues in the shorn wool if the sheep had already been treated off-shears or in short wool. This option is rarely cost-effective. See below for situations it may suit.
Option 2: Treat short wool sheep immediately
1. Sheep introduced with less than 6 weeks wool: Apply a short wool treatment (choose a product suitable for the time since shearing).
2. Quarantine for the required period after treatment, as shown on the product label.
Note: This option may produce high chemical residues in the shorn wool if the sheep had already been treated off-shears or in short wool. Use another option for sheep with longer than 6 weeks wool.
Option 3: Quarantine and decide treatment at the next shearing
1. Quarantine introduced sheep and check for lice when they are next being shorn.
2. If lice or signs of lice become evident by shearing OR the sheep were introduced less than 6 months before shearing, then apply an off-shears/short wool treatment at shearing to the introduced mob and continue quarantine for the required period after treatment, as shown on the product label.
3. If no lice or signs of lice are present at shearing AND the sheep were introduced at least 6 months before shearing, do not treat.
Option 4: No quarantine and decide treatment at the next shearing
1. Do not quarantine introduced sheep—if lice are present, this will allow them to spread to your flock—and check for lice when they are next being shorn.
2. If lice or signs of lice become evident by shearing OR the sheep were introduced less than 6 months before shearing, then apply an offshears/short wool treatment at shearing to your entire flock.
3. If no lice or signs of lice are present at shearing AND the sheep were introduced at least 6 months before shearing, do not treat.
*Option 1, despite being the best option for biosecurity, is rarely cost effective. It best suits these situations:
• When the introductions are few in number, such as purchased rams or strays collected from the neighbour.
• When the consequences of lice spreading to your existing flock are more serious than just the cost of fleece damage and treating the flock next shearing, for example, a stud breeder may have a reputation to protect.
• When the introduced sheep are obviously lousy and your ability to isolate them from the existing flock is poor.
• When your sheep have been lice-free for many years and you want to completely remove any chance of lice introduction from external sources.