The risks associated with a fatal cattle disease, which is common on Pembrokeshire farms in the autumn, could be reduced if farmers prevent youngstock from accessing freshly sown pastures.

Blackleg is triggered when cattle eat bacterial spores present in soil.

The National Animal Disease Information Service has urged farmers to be aware of the signs, so that action can be taken to prevent further cases.

NADIS vet Mike Howe, who is based in Pembrokeshire, said cases of blackleg often increased when animals moved to new pastures.

"The disease is most commonly seen in calves aged between six months and two years. Occasional cases are seen in adults and it can occur in younger animals, particularly if they have not had sufficient colostrums,'' he says. "Disease is definitely more common in animals that are growing well.''

In a NADIS report written by Richard Laven, manager of the Scottish Agricultural College's Surveillance Centre, lameness and a bloody discharge from the nose and mouth are suggested as two of the clinical signs of blackleg.

But sudden death in an apparently normal animal is the most common sign. In a few cases the first indication is tongue and throat swelling.

"In very early cases, very high doses of penicillin may prevent death but the extent of muscle damage means that in most cases this will not be economic,'' said Mr Laven.

Vaccination is suggested as the only effective means of controlling blackleg. Mike Howe said the main choice was between vaccination against the bacterium, Clostridium chauvoei, alone or with vaccines that are effective against other clostridial disease. "A farmer should ask his own vet for advice,'' he explained.

"Vaccination takes ten to 14 days to become effective so it's best to vaccinate before a problem occurs or a risk period is encountered.''

* Research by the National Animal Disease Information Service, a network of veterinary practices and colleges monitoring diseases in the UK livestock industry, is sponsored by the Milk Development Council, the Meat and Livestock Commission, Elanco Animal Health and Intervet.