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by Jenny Cotter, Department of Agriculture and Food Western Australia
The prevalence of lice in Australian sheep flocks has a long-term base average of about 20-40%, but the proportion of flocks infested can be much higher in some areas. An apparent increase in the prevalence of lice in recent years has raised grower and industry concern about lice. New infestations of lice can be avoided, but this requires careful planning, vigilance over management procedures, stock-proof fencing and preventative measures. It is worth investing time and effort in biosecurity processes in order to have a louse-free flock. Once safeguards are established, they soon become part of normal management.
Every enterprise is different and developing a lice biosecurity plan requires in-depth consideration of all the factors affecting the louse status of a property. Good biosecurity will not only prevent the introduction of lice and the consequent costs, but avoid problems from introducing lice that are resistant to specific chemical treatments.
The first step is to decide that preventing lice is a priority and that adequate time and resources will be committed to ensure this occurs. Once a lice biosecurity program is established on the property, it should be reviewed and assessed at least every two years. The main area to consider is the risk assessment (see below) as external risk levels may change over time. For example, a neighbouring property may become infested or may increase sheep trading, thus increasing the number of new sheep brought onto the property and the chance of introducing lice.
A basic knowledge of lice biology and how lice spread can help identify possible means of lice introduction to a property and assist the development of an effective biosecurity plan. Detailed information on the biology of sheep lice, how they spread between sheep, sources of infestation and the pattern of build-up in lice populations over time is available in the LiceBoss article Biology of sheep lice.
With all introductions, but particularly when sheep lice prevalence is high, it is important to take steps to avoid bringing lice onto a property when buying or agisting sheep, including rams. The other major source of lice is stray sheep, which can often enter and leave the flock undetected.
Collaboration with immediate neighbours and local area farmers can greatly reduce the risks of lice being introduced. Advisers may be able to provide technical advice to assist local lice action groups.
By identifying high risks and implementing minimization strategies the risk of lice and associated costs will be greatly reduced.
Straying sheep, either other people’s sheep straying onto your property or your sheep straying, contacting infested sheep and then returning to the flock, pose a very high risk as they may not show obvious signs of being infested. Without close surveillance, these sheep may remain undetected for a significant period of time. Maintaining sheep-proof fences is the best way of reducing the risk from strays and it is often said that the best form of lice control is a good pair of fencing pliers.
The second major means of introducing lice is on purchased or agisted stock, which may not show obvious signs of lice. This may be particularly so where sheep have been recently shorn, so that rubbing is not readily evident or where a previous treatment has suppressed but not eradicated lice.
Rams pose a frequently overlooked risk, as they are often purchased close to joining, which restricts the time available to monitor for signs of lice. It is important to have confidence in your ram source by discussing the recent lice and treatment history of rams.
All purchased sheep should travel with a National Sheep Health Declaration (NSHD) detailing whether there has been any evidence of sheep lice at or since the last shearing, the date of last shearing and the name and date of any external parasite treatment used.
Table 1 gives a broad outline of the level of risk associated with purchased sheep.
Research has shown that lice may survive for up to 10 days on shearer moccasins. If shearers have come from a property where lousy sheep were shorn, ask them to change clothes and moccasins before entering your shed. Lice may also survive for up to 3 weeks in wool left in pens or on the floor of shearing sheds. Although possible, the risk of lice introduction by either of these methods is low compared to that from straying or introduced sheep.
Table 3 indicates positive actions for use in avoiding possible non-sheep transmission.
Consider the factors that pose the greatest risk to your enterprise and apply preventative measures or change management strategies, that is, avoid or minimise high-risk activities to greatly reduce the risk of introducing sheep lice.
The source of stock (i.e. stray, purchased, agisted etc.) will influence the preventative action that should be taken. To minimise the spread of lice, infested mobs should be isolated from the rest of the flock as soon as lice are found.
By developing and implementing a stock introduction policy, the risks of introducing lice can be greatly reduced, (see Stock introduction and quarantine policies, below).
The following table can be used as a guide for introducing stock. When stock introductions are from a low-risk property, then quarantine should be all that is required. When stock are purchased from a high-risk property, quarantine and/or treatment must be used.
An important first step before introducing any sheep is to check for signs of rubbing followed by close inspection of the rubbing sheep for the presence of lice. It can be difficult to detect lice in sheep with less than 6 months wool, particularly if they have been treated and there is still the possibility that lice may be present even if they are not found at this time.
Table 1. Risk categories for different sources of purchased sheep.
|High Risk||Low Risk|
Table 2. Guidelines for preventative and corrective action relating to introduced sheep.
|Introduced stock—purchased (incl. breeders) or agisted|
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
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: Treat orally; or shear and treat topically immediately*
Note: This option may produce high chemical residues in the shorn wool if a topical product is used and the sheep had already been treated off-shears or in short wool.
This option may not be cost-effective. See below for situations it may suit and how to assess the cost.
Option 2: Treat short wool sheep immediately
Note: this option may produce high chemical residues in the shorn wool if the sheep had already been treated with a topical product 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†
Option 4: No quarantine and decide treatment at the next shearing†
All options assume that you apply any oral or off-shears/short wool topical treatments according to label instructions (including within the correct time since shearing, where applicable) to all sheep in the mob or flock and maintain the necessary period of isolation after treatment as directed by the product label.
*Option 1, despite being the best option for biosecurity, may not be cost effective especially if shearing is required. It best suits these situations:
To weigh up Option 1 for your situation:
When estimating the cost of fleece damage using the Long Wool Tool you will need to make assumptions about the level of rubbing and when it might appear, both in the introduced sheep (if no rubbing is currently evident) and in your existing flock (which could vary considerably). The extent of rubbing that will appear in your flock, if lice spread to them, will depend on how lousy the introduced sheep are, how many and which of the introduced sheep are exposed to your existing sheep (as they will have different levels of infestation) and when the contact takes place before the existing sheep are shorn. You might consider a number of scenarios, such as a worst-case scenario where the level of rubbing is high well in advance of shearing, and also a moderate and a light level of rubbing in your main flock, and estimate how likely these scenarios are. Weigh these up against the costs associated with an early shearing and treatment.
†In options 3 and 4, also check for lice each 2 months leading to shearing. If lice become apparent before the next shearing, the introduced sheep and any that they have mixed with may require an interim long wool treatment to suppress lice. Consult the Long Wool Tool to see if this is warranted. As long wool treatments cannot eradicate lice, an off-shears/short wool treatment will also be required at next shearing. Different long wool treatments are registered for different lengths of wool and for different times until shearing. Consult the Products Tool or product label to choose a suitable product.
Options to prevent non-sheep transmission
Although the risk of lice from the sources in Table 3 is relatively low, these factors should still be considered to help in keeping a property free from lice.
Table 3: Recommended options to prevent possible introduction from other sources.
|Risk factor||Recommended action|
|Shearer’s clothing||Discuss risk with shearers. If lousy sheep have been shorn at the previous property, request that precautions be taken to avoid spread of lice on clothing or footwear.|
|Wool in sheds||Avoid moving clean sheep through sheds for at least 4 weeks after lousy sheep.|
If mobs were known to be lousy at the time of treatment, then check them for signs of rubbing every 3 months following treatment to check treatment effectiveness. See Monitoring sheep for lice for directions on how to effectively inspect for lice. Be aware that causes other than lice may lead to rubbing (e.g. grass seeds, itch mite etc.) and that breeds such as Damaras and Dorpers may show signs of rubbing when the fleece is being shed. See Causes of rubbing in sheep. There are currently two recommended types of monitoring—paddock and yard.
Carry out paddock inspections at regular intervals from six months after shearing for signs of rubbing and biting. Lice infestations may be indicated if sheep are increasingly rubbing and biting at wool.
Inspect sheep when they are yarded for other procedures, such as drenching and crutching. Inspect at least 10 of the sheep with the worst rubbing by parting the wool for 10 cm in at least 10 different places per side.
Should an infestation be confirmed, isolation of the flock will limit spread. Use long wool treatments to control lice until shearing occurs. Carefully research available chemicals and application types for undertaking treatment so as to achieve good control, or eradication in the case of a short wool treatment, and follow the label carefully to achieve best effects; see the LiceBoss Products Tool.
Note that many products do not provide significant protection against new infestations. Chemicals claiming a protective period will have this information stated on the label.
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