Lice in Sheep
Lice infestation in sheep is primarily caused by the biting louse Bovicola Ovis.
Important facts about biting lice
- The entire life cycle occurs on the sheep
- It takes about 21 days from egg production to become mature adults
- They feed on skin debris and wool scale
- They prefer it cool and dark hence numbers increase over winter and in long woolen sheep. Most summer shorn sheep will be devoid of lice
- The ‘effective grazing’ area for the louse increases with bigger sheep (big surface area),more wool, fineness of wool and crinkliness of skin (esp. Merinos)
- Spread only occurs with dose contact between sheep e.g. yarding, lambs suckling, rams mating, mobbing behavior (Merinos), camping together in sleep camps esp. in cold weather
- Shearing removes about 30% of lice
- Found mainly in the shoulder/neck/wither areas
- Lice are pale brown in colour and about 1.5mm long.
Effects of lice
- Irritation causing rubbing
- Decrease in yield and luster of wool
- One estimate is a cost of 20c per 1kg of wool
- May pre-dispose to fleece cotting
- Cockle in pelts is reduced dramatically if effective dipping is undertaken resulting in saving for the leather industry
- Lice DO NOT CAUSE ILL THRIFT but can increase dramatically in ill thrifty animals.
- - Sheep rubbing
- - Part wool in at least 10 sites in shoulder, neck area and check for lice
- - Examination of fleeces post shearing - ask the rousies.
Problems associated with treatment
- Pourons can fail for several reasons:
- Not applied to neck and withers where lice reside and only applied on 1 side of body - use T bar running from the neck to tail along midline.
- Under dosing due to underestimating sheep weight and not allowing for the increase in ‘effective grazing area’ in long wool sheep.
- There are some synthetic pyrethroid (SP) resistant lice
- SP’s can take 6-8 weeks to kill lice so non treated animals in contact within that period can become infected e.g. lambs or ewes.
- - Saturation dipping with just about any insecticide will kill all lice
- Some fly controls also kill lice so check to avoid overdosing your sheep
- Lice are easiest to kill on short wool sheep in summer when numbers are low. Long wool sheep in Winter with large lice numbers make treatment difficult.
- Treat the rams
- Treat all introduced sheep
- The withholding time for wool is voluntary. If you get an infestation you will need to treat and only the meat withholding is obligatory.