livestock ‘n’ animal health


Sheep External Parasites by Bruce Richards BVSc DBR MRCVS


Bruce Richards BVSc DBR MRCVS


With a primary interest in fertility, particularly bulls and optimizing dairy herd productivity, Bruce is one of six dedicated large animal vets at Paragon.


CARLISLE HOUSE, TOWNHEAD ROAD, DALSTON, CARLISLE, CUMBRIA, CA5 7JF TEL (01228 710208) FAX (01228) 711960 E-MAIL vets@paragon.com WEB www.paragonvet.com


Parasitic infestations in the skin and fleece of sheep are still very common. Some parasites can cause disease in their own right such as scab and fly strike whereas other parasites such as ticks are mainly important because they are capable of transmitting diseases such as tick borne fever. It is important with all external parasitic diseases of sheep to try and identify the parasite(s) involved. This will normally involve the vet examining the fleece and taking a skin scraping. Once you know the cause, not only can the correct treatment be used but also a suitable control program can be put in place to prevent recurrence in future seasons. In some circumstances it may even be possible to totally eradicate the parasite from your flock for good.


Sheep scab: This is caused by a burrowing mite called psoroptes ovis. It is no longer notifiable and unfortunately is very common with most signs seen in the winter months. These mites cause small pustules on the surface of the skin, which produce the moist scab typical of this disease. Sheep scab is an intensely itchy condition and affected sheep will bite and pull at their own fleece and can rapidly lose body condition. Mites often go dormant over summer so infection is often brought in on replacements or store lambs that look clean. Mites can survive off the sheep for up to 17 days and so can be present on creep feeders and gateposts where affected sheep have been scratching.


Lice


Again this disease is mainly seen in winter and can be confused with scab. There is normally not the same degree of damage to the skin and the lice are bigger than mites and visible to the naked eye on close examination. Animals in poor body condition are much more susceptible to lice infestations which can then cause further weight loss and debilitation.


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Generally not as intensely itchy as scab. Not all scab treatments will protect against lice.


Fly Strike/Maggots Well known to all sheep owners, this disease increases in prevalence during the summer months as temperatures rise. Unshorn or dirty sheep are much more prone to disease, which normally starts around the tail but can affect any part of the skin. The disease rapidly progresses if left untreated. Affected sheep initially appear agitated trying to bite at the affected area but, especially if a large area is affected, they may simply appear dull and listless. Timely shearing, dagging and preventative treatments are vital to control this disease, which is a major welfare issue.


Other Causes of Skin Disease in Sheep • Orf (caused by a virus) • Dermatophilosis (or lumpy wool disease caused by bacteria often after a prolonged period of wet weather and muddy conditions)


• Ringworm (a fungal disease) • Facial Eczema (bacterial infection around the face. Usually secondary to some form of trauma such as rough or inadequate trough space. Often a complicating factor with orf)


• Scrapie – a notifiable disease related to (but not the same as) BSE in cattle.


Biosecurity and Quarantine. If you are bringing sheep onto your holding it is important to remember they may well be carrying unseen parasites with them. Ideally therefore they should be quarantined, treated and kept separate for three weeks after arrival on farm. Good fencing is vital as many scab outbreaks occur after unwelcome visits from stray sheep. Also remember that some of these parasites can survive off the sheep for up to three weeks and can be transferred on clothes and equipment if not thoroughly cleaned and disinfected.


Prevention and treatment of external parasites. Dips, pour-ons or injection? In all cases it is important to remember to treat all sheep within a flock at once. Organophosphate dips are probably the most effective way to treat and prevent fly-strike, ticks, lice and scab. However, it is vital that the dip is made to the right concentration, is clean and that the sheep’s head is plunged into the dip to ensure that scab mites (which tend to hide in the ears) are completely eliminated. The use of the dips is now regulated and only trained and licensed operators wearing suitable collective clothing should use these dips. Pour-ons, if used as per manufacturers recommendations can give good protection against fly-strike, lice and ticks but are not effective against scab. They should not be used as a quarantine treatment. Avermectin injections such as ivomec, dectomax and cydectin will kill sheep scab but not all lice. The dose and duration of effect varies between products, so follow specific treatment advice from your vet or s.q.p. for effective control.


In summary… • Avoid buying sheep from unknown sources


• Quarantine and treat new arrivals • When you treat your flock, treat all at once


• Keep sheep fleeces clean by having a worm/cocci control plan and by timely shearing/dagging


• Put in place regular treatments during summer to prevent fly strike.


• When you have a problem, get the sheep examined to identify the parasite involved.


• Work with your vet to use the right product, at the right dose, at the right time.


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