The sheep body louse is a small, pale to red/brown insect with a broad head and chewing mouthparts, hence they are often called ‘ Chewing or biting’ lice. They feed on skin debris and hair are must not to be confused with sucking lice which are not a problem in the UK.
The clinical signs of chewing lice can be confused with that of sheep scab (Psoroptes ovis) so it is very important to get a professional diagnosis before deciding on the treatment to be used. The sheep are irritated by the Lice and the scratching and rubbing will damage the fleece and hide. Immune responses to Lice can result in the nodular skin defect known as “cockle”, downgrading the value of the leather.
Heavy infestations of lice are usually associated with animals in poor health because they seem to be able to exploit such sheep.. In contrast, in fit, healthy flocks no significant differences in lambing % and lamb weights at weaning between louse infested and louse-free sheep have been observed. Chewing lice can therefore be a significant indicator of underlying welfare problems within a flock.
The prevalence of chewing lice is seasonal, with most cases occurring in the winter and the severity of the infestation appears to depend on the breed, fleece length and overall health of the host together with the temperature. Lice populations tend to thrive during the winter and are lower in the summer. Shearing will reduce populations by 30-50%.
The table below shows the products currently available for the treatment of Chewing Lice.
|Chemical||Trade name(s)||Other ectoparasites covered||Meat withdrawal period (days)|
|Blowfly, Ticks, Headfly||28|
|Lice (treatment only), Ticks, Headfly||8
|Diazinon||Osmonds Golden Fleece||Scab, Ticks, Keds Headfly||49|
|Diazinon||Paracide 62||Scab, Ticks, Keds Headfly||70|
- Always get a diagnosis before treating
- The Endectocides do not treat Chewing Lice
- The use of the pour-on products should be avoided in fully fleeced sheep because this results in a less effective treatment and increases the risk that resistance to the product will develop in the Lice.
- The best results are when a pour-on is applied ‘off shears.