| Information sheets | | | Elsenburg infopaks | | | Animals, management: 18 |
Sheep and goat lice
The major lice affecting the South African Wool clip are the sheep and goat body lice namely Bovicola ovis and Damalinia limbata. The parasite feeds on the fatty secretions covering the skin surface. Sheep and goat lice cause intense irritation to infested animals resulting in pulled and clotted wool especially around the flanks.
Fig 1: The sheep body louse (Bovicola ovis). Actual size 1.5 - 2mm
The adult female lays eggs, which are attached to wool fibres. These hatch after 9 - 10 days, developing through three nymphal stages before reaching adulthood approximately three weeks later. Egg laying can occur in a further 3-4 days so that the entire life cycle can be completed within 34 days when conditions are favourable. Adult lice live for approximately 1-2 months but under certain conditions can survive for up to 14 weeks.
The economic implication of lice to the Australian sheep industry in 1990 - 1991 was estimated to be over $300 million. Lice reduce wool income by decreasing fleece weight and by causing a decline in fleece quality. Infested goats and sheep rub and bite at the fleece causing further damage. This rubbing may also predispose the sheep to flystrike, increasing economic losses.
Trials in Australia have shown that even a light infestation will result in a loss of R7.47 per head (based on 1908c/kg clean) and heavy infestations can lead to losses of R42.75/head!
Sheep and goat lice are obligatory parasites. Clean sheep and goats can only get lice from direct contact with infested sheep or mechanical transmission (clothes, vehicles etc.). Lice infestations can build up rapidly on individual sheep and goats and spread quickly through a mob.
It was demonstrated that the introduction of two lousy sheep into a mob of fifty lice free animals, resulted in all sheep being lousy within 16 months. By that time about half of the animals will carry a medium to heavy infestation.
In order to achieve adequate control of both Damalinia limbata and Bovicola ovis on sheep and goats correct application of the products are essential.
Fig. 3: Fleece derangement caused by lice
Traditionally after shearing, dipping with either organophosphate (e.g. Dazzel nf) or pyrethroid (e.g. Zeropar) containing dips, controlled the lice sufficiently, but in recent years resistant populations emerged and proper control is only achieved by the use of Insect growth regulators (IGR)
As Insect growth regulators (e.g. Triflumuron (Zapp)) only affects the moulting process, adult lice are not killed. It may therefore take up to 14 weeks for the adult lice to die out. A rapid decline in lice numbers is seen over several weeks achieving control of moulting larvae and nymphae.
Every product, no matter how effective must be used correctly to achieve and maintain a lice free flock. Attention to detail is important.
- Start with a complete muster. Lice are only acquired from other infested sheep or goats.
- Clean shearing is important. If cotted fleeces, grass seeds, lumpy wool or fly strike prevent clean shearing, lice control by any method will be poor.
- Correct application of selected product
- IGR containing products protects against reinfestation
- Treated animals should not be mixed with lice free or lousy animals.
- Any new animals should be treated and isolated from the flock.
