Hard-to-spot maedi visna on the rise, says vet
DIFFICULT diagnosis could be masking increased incidence of maedi visna infection in commercial ewe flocks across the country.
Geoff Pritchard of the Veterinary Investigation Centre, Bury St Edmunds, Suffolk, told producers at a sheep night held in Newmarket by the National Sheep Associations eastern region that incidence of this debilitating sheep disease was on the increase.
Dr Pritchard said MV cases were easy to overlook because secondary infections – pasteurella pneumonia, lungworm, and pulmonary adenomatosis – often masked the underlying cause.
"At first glance MV can look like pasturella pneumonia," he explained. Also many affected animals were culled without detailed diagnosis.
Although the disease was of most concern to pedigree flocks selling breeding stock, the trouble for commercial producers was that it could knock two years productive life off ewes.
"The main concern is its insidious nature – it eats away at the long-term viability of ewes," he said.
MV had a long incubation period which meant that 60% of the flock could be infected before clinical signs of the disease which had two main forms – maedi and visna – showed. Signs of maedi, the most common type in the UK, were pneumonia and poor breathing, often associated with secondary infections; visna was a wasting and nervous disease.
MV could be transmitted through close contact with infected animals and inhalation via droplets from the nose and mouth. Lambs could pick up infection through colostrum. It infected sheep at any age, but clinical disease was not usually seen until sheep were three to four years old.
Dr Pritchard recommended producers suspecting disease in their flock consult their vet and blood test the ewes in question.
• The Sheep and Goat Health Scheme is to introduce a MV monitoring scheme in April for commercial producers. This should reduce costs because it will require testing of a smaller proportion of the flock than the existing scheme and only one qualifying blood test. Details: (01908-844312).
Where temperatures have started to increase, coccidiosis may cause problems in early lambing flocks with housed lambs, especially if ewes were not treated, according to UK vet parasitologist Gordon Graham.
Infection is also seen in lambs born outside, he warns, when they are three to eight weeks old, and especially in wet, dirty conditions coupled with high stocking rates. Symptoms include scouring, a dry,
harsh coat, rapid breathing and weight loss.
Prevention depends on good husbandry and drugs included in sheep feed, says Scottish Agricultural College vet Brian Hosie. He advises that troughs and water bowls are kept clean – and well above the bedding as the housing period progresses.
"Young lambs are highly susceptible and should be kept separate from older lambs until they are 10 weeks old."
MAEDI VISNA CONTROL
• Test and cull before pneumonia and wasting develops.
• Consider taking lambs from their mother at birth.
• Flock can be culled and replaced with clean stock.