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Watch Replacements and Store Lambs When Grazing This Winter

10 December 2014

Store lambs could be particularly susceptible to parasites this winter, so monitor faecal samples, farmers are being told.

September was dry and October was wet for much of the UK, meaning store and replacement lambs could be at risk from parasitic gastroenteritis. 

National Animal Disease Information Service (NADIS) veterinarians have advised that liver fluke and sheep scab may also need vigilance, although regional variation should be accounted for. 

Parasitic Gastroenteritis (PGE)

  • Outbreaks of trichostrongylosis in store and replacement lambs are a risk if mild wet weather extends into December with farmers not accustomed to drenching sheep so late in the year.
  • Continue to monitor worm egg counts of pooled faecal samples.

Trichostrongylosis in store and replacement lambs is a risk if mild wet weather extends into December.

Liver Fluke

  • After closantel treatment in November in all regions, fluke treatments can probably be delayed until January when closantel or nitroxynil could be used.
  • Albendazole and oxyclozanide are effective from 10-14 weeks post infestation and can be used when treatment is recommended to remove adult flukes in late spring (often in May).
  • Treatment in May will further limit pasture contamination by fluke eggs reducing the risk of disease later in 2015.

Skin Infestations

Lice in sheep

  • Louse populations are highest in sheep during late winter.
  • Spread occurs by direct contact.
  • Lice infestations are widespread in most sheep flocks.
  • Use of plunge dipping for other reasons, such as control of sheep scab, cutaneous myiasis and headfly problems, effectively controls louse infestations.
  • Louse infestations can also be controlled with topical application of high cis cypermethrin or deltamethrin but these are best used soon after shearing.

Louse populations are highest during late winter and may cause disrupted feeding patterns, fleece damage/loss, and self-inflicted trauma.

Poor flock husbandry and a welfare concern - heavy louse infestation affecting a ewe in poor condition.

Sheep scab

  • Sheep scab is caused by the mite Psoroptes ovis; cattle are rarely affected.
  • Mites are most commonly transmitted by direct contact with infested sheep.
  • Sheep scab can be introduced to a flock by carrier sheep, including purchased animals, sheep returning from grazing, and strays especially on common grazing.
  • Recently infected sheep may not show clinical signs of sheep scab.
  • In most sheep, scab is characterised by intense itching, with repeated rubbing of the shoulders and flanks along the ground or against fences, foot stamping, clawing at the flanks, and biting the shoulders.
  • Tufts of wool are characteristically seen on fences and hedges.
  • Animals are often seen at different stages of the disease within affected flocks.

Frequent rubbing against fences may indicate sheep scab infestation but is also commonly seen with louse infestations.

Wool along the length of this fence is not normal and warrants immediate investigation.

Animals are often seen at different stages of the sheep scab infestation within affected flocks.

Neglected sheep scab; wool is lost and the skin becomes thickened and covered with scabs.

Treatment of Sheep Scab

  • Treatment should be discussed with your veterinary surgeon.
  • Plunge dips containing dimpylate (active substance) kill scab mites within 24 hours and affords residual protection for several weeks.
  • Plunge dipping also treats lice, blowflies, and ticks present on the host.
  • Macrocyclic lactones (avermectins and milbemycins) given by injection can be effective against sheep scab mites, keds and sucking lice, but have no value for the control of blowflies, chewing lice, chorioptic mange or ticks in sheep.
  • It is essential that all sheep are gathered and correctly treated.
  • Handling pens and fields should be considered as a source of re-infection for at least 17 days after removal of untreated sheep.
  • All additional introduced animals should be treated and quarantined for sufficient time.

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