LOUSYOUTLOOKASPESTSPREADSTHROUGHOUTUK
LOUSYOUTLOOKASPESTSPREADSTHROUGHOUTUK
LICE infestation in sheep is increasing, both in terms of number of stock affected and geographical spread, with more lowland sheep flocks becoming susceptible.
Recent research undertaken by Peter Bates, VLA entomologist, shows that chewing lice are no longer confined to hill flocks in Scotland and Wales but are spreading throughout the country, even into the Midlands and south of England.
He studied six louse-infested flocks throughout the country between February 1999 and April 2000. Results show 42.3% of sheep were carrying light infestation – below 20 lice/sheep and 16.7% of sheep were heavily infested – over 100 lice/sheep. The majority of reported infestations occurred between January and April.
"Compulsory dipping almost eradicated chewing lice, but with removal of dipping, OPs and the increased use of less effective injectable treatments, chewing lice have become prevalent," explains Dr Bates.
The clinical symptoms of chewing lice, such as itching, rubbing and biting of the fleece, have also been confused with sheep scab and this has led to incorrect treatments being used against lice, resulting in possible resistance problems, he adds.
Tempoary reduction
"Use of systemic endectocides against supposed scab infestation will temporarily reduce lice populations, but high numbers will soon recover."
The only effective treatment against all types of lice – chewing, blood-sucking and foot lice – is to use an OP dip, SP dip or an SP spot-on or pour-on, which will also cover other ectoparasites. In Australia, where fleeces are more highly valued, treatment follows shearing, which in itself reduces lice populations by 30-50%.
Research also shows lambs and older stock in poor health and/or kept in unhygienic conditions seem to be more susceptible to lice infestation. This also applies to cattle. In general a low body condition score sheep suffers a higher lice population.
"It is not certain whether lice lower animal condition score or whether they exploit an animal already out of condition, but either way they are an indicator of underlying welfare problems within a flock," he says.
Lice also seem to prefer living on long-fleeced sheep where a moist and warm microclimate exists which is ideal for louse reproduction, even though this is a slow process. Populations will spread gradually among closely housed sheep during the winter, he adds.
Infestation can cause considerable, yet unmeasurable losses, from unthriftiness, retarded growth and damaged wool.
Lice in sheep must be treated to avoid losses from unthriftiness, retarded growth and damaged wool.