Livestock
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Parasite control
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| Healing lesions |
WHILE sheep scab is the most important ovine skin infestation, farmers must also be aware of the other ectoparasite infestations that can affect their sheep causing financial loss and welfare concerns.
Control of all ectoparasites infestations can largely be achieved by strategic treatments and strict biosecurity although these principles of disease control appear to have been largely forgotten in the 15 years since the cessation of compulsory plunge dipping. A control programme must be included in all veterinary flock health programmes and implemented before the major risk periods.
Headfly
In the UK, headfly can present a major problem during the summer months. Grazing patterns are disturbed and affected sheep often isolate themselves and remain in shade where available. They may stand with the head held lowered with frequent head shaking and ear movements. Alternatively, sheep adopt a submissive posture in sternal recumbency with the neck extended and the head held on the ground (Fig 1). Kicking at the head often greatly exacerbates damage caused by headflies and such action may also traumatise the skin of the neck and ears (Fig 2). The impact of headfly worry and interrupted grazing is clearly shown in Fig 2 by comparing the affected sheep in the foreground with another sheep managed in the same group. Fleece quality is adversely affected and the loss of body condition will reduce ovulation rate and subsequent litter size costing the farmer money.
Topical emollients and antibiotic preparations are not usually necessary and skin wounds heal well provided the flies are denied access to these areas. Housing is essential for sheep with large skin lesions to allow time for complete healing (Fig 3).
Pour-on fly control preparations, such as high cis cypermethrin or deltamethrin, must be applied before the anticipated headfly season and especially to horned sheep with re-application as directed by the manufacturer's instructions.
Cutaneous myiasis (Blowly strike, maggots)
Blowfly lesions may range from one centimetre diameter areas of skin hyperaemia with a small number of maggots to extensive areas of traumatised/devitalised skin causing death of the sheep.
Depressed
Adult flies are attracted to areas of faecal staining surrounding the perineum; and less commonly virulent footrot lesions, dermatophilosis lesions on the skin, and urine scalding around the prepuce.
In severe infestations the sheep are depressed and isolated from the flock. Large numbers of adult flies are seen on the fleece with maggots on the blackened skin once the surrounding fleece has been lifted clear. There is an associated putrid smell.
Affected sheep can be treated by plunge dipping using a synthetic pyrethroid or organophosphate preparation but it is more usual to treat individual infested sheep with dip wash applied directly to the struck area after first clipping away overlying wool.
Worm control measures to reduce diarrhoea and ("dagging" or "crutching", Fig 4) in May/June reduces the attraction of blowflies well before the peak of the blowfly season.
Dimpylate (diazinon) and propetamphos are effective against blowfly strike. These compounds are strongly lipophilic and replenishment of dips is important to maintain effective concentrations within the bath. The synthetic pyrethroids, including high cis cypermethrin, have a much higher human safety margin than the organophosphorus compounds and persist in the fleece for up to eight weeks.
While topical application of high cis cypermethrin pour-on preparations provides protection against fly strike, these preparations persist for only six to eight weeks at the site of application and require re-application in most situations.
The insect growth regulator, cyromazine, applied before the risk period is very effective against blowfly strike for up to 10 weeks after topical application and dicyclanil affords 16 weeks' full body protection.
NADIS is sponsored by:
EBLEX
Merial Animal Health
Pfizer Animal Health
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