A Guide to Responsible External Parasite Control in Sheep

Transcription

1 A Guide to Responsible External Parasite Control in Sheep

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3 Contents Introduction to Guidelines Dr Peter Bates, VLA 3 Responsible External Parasite Control Peter Morris, NSA 4 Ectoparasite Control Decision Tree 5 Blowfly Strike 6 Ticks 10 Chewing Lice 12 Sheep Scab 14 External Sheep Parasites: Guidelines for Responsible Control This guide is a practical introduction to the external parasites most likely to jeopardise the welfare and productivity of your sheep: scab, chewing lice, ticks and blowfly strike. It aims to encourage better identification, and understanding, of the parasites involved their lifecycles, symptoms, the time of year at which they occur and the use of the most responsible methods of control. By preventing the misuse of chemical products, these guidelines promote a long-term approach to sheep welfare designed to minimize the build up of resistance and protect the future health and productivity of flocks throughout the UK. Dr. Peter Bates Senior Entomologist VLA 3

4 The Importance of Responsible External Parasite Control As individual sheep farmers, it is vital to give thought and planning to decisions relating to ectoparasite control. The UK flock is under severe pressure from a variety of ectoparasites and the range of preventative measures and treatments at our disposal is, and will continue to be, limited. Some of those products particularly the plunge dipping chemicals continue to be closely scrutinised and to ensure their continued availability it is vital that they are used safely, responsibly and in line with the recommendations of the Stop every Drop campaign. Using the right kind of product for the problem to be dealt with is a key decision for all sheep farmers. If we do not make strategic and considered choices, based on understanding the ectoparasite challenges facing the flock at any given time of year, then the emerging resistance issues that are becoming obvious in some areas will continue to grow and place the sheep industry in an impossible position. Using ectoparasite controls strategically, in conjunction with health planning, will not only provide the most effective control of parasites, it will also ensure the longevity of the products and save you money. NSA encourages all UK sheep farmers to adopt the principles outlined in this guide to give the best possible long-term protection to the national flock from ectoparasite infestations. Peter Morris Chief Executive, National Sheep Association January

5 Ectoparasite Control Decision Tree Follow this decision tree to identify the ectoparasites affecting your flock and select the most suitable methods of treatment. What is the problem? Itchy Sheep Veterinary diagnosis Blowfly Ticks Lice Scab Prevention Treatment Insect Growth Regulator (IGR) SP Pour-on/ Spot-on or OP Dip SP Pour-on/ Spot-on or OP Dip OP Dip or Injection 5

6 Blowfly Strike What is it? Larvae (maggots) of three species of fly commonly attack sheep in the UK: Lucilia sericata (the greenbottle ), Phormia terrae-novae (the black blowfly ) and Calliphora erythrocephala (the bluebottle ). These species are not totally parasitic and large numbers are associated with the environmentally useful tasks of faecal and carcass decomposition. Strike can be classified as wound (usually feet), body or breech. In body strike, flies are attracted to sheep by the odours of excessive sweating and/or decaying organic matter in the fleece, usually over the loins, shoulders, flanks, neck, back, throat or abdomen. In breech or tail strike, flies are attracted to fleece contaminated with urine and/or faeces and are particularly associated with scouring. Symptoms Signs of strike include agitation and dejection, foot stamping, vigorous shaking, gnawing or rubbing of the tail and breech. As infestation develops a distinctive odour is noticeable and the wool becomes matted and discoloured. If the infestation remains untreated the affected area increases and wool is shed from the centre, accompanied by signs of constant discomfort. Death will occur soon after. The smell of infestation attracts further flies. If unchecked, extensive infestations of further waves of flies can result in a quick and agonizing death. 6

7 Timing The prevalence of blowfly strike is weather-dependent, with most cases of body strike occurring during periods of high humidity or warm periods after heavy rain. In the south east of England strikes can occur any time between March and December. Breech strike depends less on weather as the moisture supplied by urine and/or scouring is sufficient for larval development. Blowflies are part of the normal flora and fauna of your farm they are there spring to autumn. Carcasses (small or large) and foot rot can increase fly numbers. Make sure all carcasses are disposed of and attend to infected feet as soon as possible. 7

8 Blowfly Strike Blowfly Lifecycle Adult flies can lay up to 3,000 eggs in 9-10 batches over a 3 week period. Eggs hatch within 24 hours if the fleece humidity is optimal. Eggs are continually being deposited on the fleece (even in hot, dry weather), but first stage larvae cannot survive in wool with a moisture content below 90 per cent. Later stages are less dependent on humidity. Total development can take 5-11 days on a carcass but only 3 days in body or breech strike or even shorter in a wound. Larvae leave the sheep to pupate in the soil and remain in the pupa for 3-21 days under summer conditions. Over-wintering pupae remain inactive until the soil temperature rises above 7 0 C. The Blowfly lifecycle Deposition of eggs in the fleece 1st Larval Stage. No mouthparts Average life cycle 2-4 weeks Fly emergence after 2 weeks warm weather Pupation 2nd and 3rd Larval Stages. Mouthparts very active and feed constantly. 8

9 Prevention Evidence points to the possibility that some attraction factors are hereditary and breeding ewes and rams continually struck could be culled. Ewes with deformed genital openings, where urine is directed onto the fleece and ewes with narrow breeches that favour soiling could also be culled. Complete shearing temporarily reduces the risks of strike, but the susceptibility of the sheep increases as the fleece grows. Routine crutching and dagging is effective if started in April and repeated every four to six weeks. Tail docking may also reduce the incidence of strike. Prevention is the best form of control. Strike can be prevented through the use of pour-ons containing the insect growth regulators (IGRs) cyromazine or dicyclanil, however these products will not cure existing infestations. Treatment of existing strike Cure and protection can be attained using a diazinon based plunge dip or a synthetic pyrethroid (SP) based pour-on containing alphacypermethrin or cypermethrin. Spot-on products containing the SP deltamethrin will cure existing infestations but will not protect against further attack. 9

10 Ticks What are they? Ticks (Ixodes spp, Haemophysalis spp, Dermacentor spp) can have significant effects on sheep welfare and production, particularly through the transmission of louping ill, lamb pyaemia ( cripples ) or tick borne fever (TBF). Symptoms Timing Ticks are generally active from March until October, depending on the weather. 10

11 Tick Lifecycle The tick life cycle includes egg, larva, nymph and adult (male or female). The entire life cycle can take 1 to 5 years depending on the weather and availability of suitable hosts. Ticks feed on blood seeking suitable blood vessels in/on the ears, groin and armpits of the sheep. Ticks feeding on sheep are mainly adults. Adult ticks will also feed on cattle, horses, deer, etc. Nymphs generally feed on smaller hosts (foxes, rabbits etc) and larvae feed on even smaller hosts (birds, mice, etc). Each stage feeds only once, engorging on blood for 2 to 15 days and then dropping off into the environment to digest its bloodmeal and moult into the next stage. Ticks require dense moisture retentive habitats, eg. rough grazing, moorland, heath or woodland. The thicker the vegetation the heavier the tick population. Ticks are becoming more abundant due to changes in farming practice, climate change and acaricide resistance. Adult ticks will also feed on humans where they can transmit Lyme Disease a serious and potentially debilitating disease. Prevention Prevention is the best form of control. Ticks can be prevented through the use of a diazinon based plunge dip or a synthetic pyrethroid based pour-on containing alphacypermethrin or cypermethrin or spot-on products containing the SP deltamethrin. 11

12 Chewing Lice What are they? Chewing lice (Bovicola ovis) are small, pale to red/brown, flat, insects, feeding on skin debris and hair, living within the centimetre of wool closest to the skin. They do not produce a definite scab lesion and can be found anywhere on the sheep. Symptoms Infested sheep rub and scratch and the fleece appears rough and pulled, with numerous loose strands of wool. Sheep can bite and nibble at the fleece. There is no biting reflex on handling. Heavy infestations are associated with sheep in poor health. Lice populations are influenced by body condition; the lower the body condition score the higher the population of lice. Thus, chewing lice are a significant indicator of underlying welfare problems within a flock. 12

13 Timing Lice are generally seen between January and March. Chewing Lice Lifecycle Lice live their entire lives on the sheep, introduced by contact or purchase of infested stock. Lice can, however, live off the sheep for 16 to 17 days in tags of wool, clothing, barns or livestock transport. Prevention Quarantine all incoming stock for at least 3 weeks. Ensure fencing is sound prevent straying on or off. Disinfect livestock trailers after use. Remove all debris (wool etc) from contaminated housing and do not re-stock for at least three weeks. Treatment Act as soon as you see the sheep rubbing and scratching. Have the sheep examined by your vet he/she will identify any parasite and advise on treatment. The cost of not involving a vet will be far more than the cost of veterinary inspection! Sheep can also have mixed infestations of sheep scab and chewing lice. Chewing lice can be controlled by using a diazinon based dip or synthetic pyrethroid (SP) based pour-ons or spot-ons using alphacypermethrin, cypermethrin or deltamethrin. 13

14 Sheep Scab What is it? Sheep scab is caused by a tiny, pearly-white mite (Psoroptes ovis), just visible to the naked eye. Mites live on the skin surface, causing a skin allergy to their droppings. Initially the scab is very small (less than the diameter of 1p coin). As the mites multiply the scab spreads, eventually covering the whole sheep. Mites can be found around the edge of the growing lesion. Symptoms Early disease is difficult to spot animals look and behave normally. As the scab spreads the sheep becomes increasingly irritated, excessively rubbing and scratching and digging with their back legs. After about 10 to 15 weeks the scab covers the entire animal and the wool can fall out, revealing a dry, scabby skin beneath. By this time scab has spread throughout the flock making control a costly exercise! Infested animals can demonstrate a violent biting reflex on handling (similar to scrapie), sometimes leading to epileptiform fits. 14

15 Timing Scab can be found throughout the year, but the majority of cases occur between October and March. Sheep Scab Lifecycle Scab mites live their entire lives on the sheep, introduced into a flock through contact or purchase of infested stock. Mites can however live off the sheep for 16 to 17 days in tags of scabby wool, clothing, barns or livestock transport. Prevention Prevent by quarantining incoming stock for at least 3 weeks. Ensure fencing is sound to prevent straying on or off. Disinfect livestock trailers after use. Remove all debris (wool etc) from contaminated housing and do not re-stock for at least three weeks. Treatment Don t wait for wool to fall out - act as soon as you see the sheep rubbing and scratching. Ask your vet to examine the sheep to identify any parasite and advise on treatment. Not involving a vet will be far more costly than prompt veterinary inspection! The signs of scab can be confused with those of lice. Resistance may occur in both ectoparasites if they are not professionally identified and treated. Sheep can also have mixed infestations of sheep scab and chewing lice. Sheep scab can be controlled by using a diazinon based dip or by doramectin, ivermectin or moxidectin based injections. Remember that injections are also effective wormers and misuse could lead to drug resistant worms consult your vet. 15

16 Sponsored by For further information contact: Novartis Animal Health UK Ltd., New Cambridge House, Litlington, Nr. Royston, Hertfordshire SG8 0SS Tel: FAD 730 JAN 2007