Checking sheep for lice

Sheep lice magnified 10 times

When to check for lice

• Check all mobs at least twice each year. At crutching and before shearing are appropriate times. In addition, any sheep seen at any time with rubbed or pulled wool should be checked.

• Check all sheep at purchase (including rams) or when brought in from other properties. Remember, lice are very difficult to find if they are in low numbers. Even if you cannot find lice, these sheep could still be infested and should be kept isolated from other mobs. It can take up to 6 months for a very light infestation to become obvious.

• Check all stray sheep and sheep returned from neighbours. These sheep are often the reason for new infestations and should be checked carefully. Lice are difficult to find soon after shearing even if sheep have not been treated. If sheep have been treated but lice have not been eradicated, it may be more than six months before lice can be easily found.

Early detection of lice allows prompt treatment of the infestation and reduces damage to the wool clip.

What to look for

Lice are most commonly found near the skin. However, the lice can move away from the skin and up into the wool when the fleece is shaded, for example, when sheep are in a shed or in close contact with other sheep. Sheep rubbing or biting at their fleece is a sign that lice may be present. However, rubbing can also be a result of irritation caused by grass seeds, fleece rot, lumpy wool, itchmite, blowfly strike or other skin diseases. A break in the wool, feeding through fences Sheep lice magnified 10 times and walking through bush or stubble can also give the fleece a rubbed appearance. To be sure that lice are present, you must part the wool and actually see the insects.

If sheep are not rubbing, it does not necessarily mean that they do not have lice. Sheep can be infested without any obvious signs of rubbing. It is extremely important to check sheep closely for lice even if rubbing is not evident.

Damaged fleece from lice

How to check for lice

Lice are difficult to see. When inspecting for lice, ensure that the sheep is in a well lit position. Make sure you know how to recognise a sheep louse and wear glasses if you need them for reading. Part the wool for about 10 cm and inspect closely for lice. It is important to check every mob on your property and to inspect as many sheep in each mob as possible. Soon after shearing, lice are most likely to be found in poorly shorn patches, under the neck and on the lower flanks. In longer woolled sheep, lice are most common along the sides and this is where inspections should be concentrated.

• If there are any sheep in the mob with rubbed fleece or which are biting at their wool, check these animals first. Check 10 parts on each side of these sheep.

• If no evidence of biting or rubbing is seen, catch sheep at random and inspect 10 parts per sheep on at least 20 animals. Inspecting more sheep will increase the likelihood of finding lice if they are present.

• Ask your shearers, wool classer and shed hands to look out for lice at shearing.

Even if you find only one louse, the flock is lousy and treatment options should be considered.

To treat or not to treat

The best time to treat sheep for lice is soon after shearing. Treating after shearing gives maximum probability of eradicating lice and minimises insecticide residues in wool. Chemical residues are not tolerated by wool processors and it is important to consider with-holding periods before deciding on a treatment option:

• treat the mob in long wool,

• shear early and treat after shearing,

• keep the infested mob separate from other sheep and treat after the next scheduled shearing.

The option taken will depend on factors including the level of infestation, time until the next shearing, discounts in the market for wool with insecticide residues and the availability of low residue treatments.

Sheep blowfly

Other parasites

Other external parasites that infest sheep, and should be distinguished from sheep-biting lice are:

Face lice and foot lice

These are sucking lice which are bluish grey in colour and usually found on the haired skin of the face and legs, on the scrotum of rams or near the wool-hair junction. They are not usually found in the fleece wool along the sides of the sheep where the biting louse is most common. They are fairly rare in SA sheep flocks. Seek advice about their treatment if they are found.

Itchmite

Too small to be seen without a microscope, these are usually beneath the surface of the skin. For definite diagnosis a skin scraping must be taken.

Sheep blowflies

A severe problem to the sheep industry, blowfly strike is not likely to be confused with lice. However, sheep that are irritated by flystrike can bite at the fleece in a way similar to when lice are present.

Ked or sheep ‘tick’

These are reddish brown and much larger than lice. They are now rare in Australian sheep flocks, although they were a problem in past times.

More information: www.liceboss.com.au