POOR quality forage could cause severe problems with listeriosis infection in sheep and result in a mortality rate of up to 10% in the most extreme cases, NADIS has warned in its latest health bulletin for Scotland.

The bacterium listeria monocytogenes grows well in less acidic pH of spoiled silage - a pH of 5.0 or under - but clinical outbreaks can occur around 14-21 days after feeding poor quality silage.

This time lapse between ingesting the bad silage and showing signs of the infection can confuse flock masters, so the advice is not to feed any bad bales to stock, but discard them.

The economic implications can be severe in the worst cases, though it is thought that less than 2% of stock will be clinically involved in an outbreak, though for those affected, mortality rate can be greater than 70%.

Clinical signs - not eating; depressed, disoriented; propel themselves into corners, into fences, under gates and feed troughs; lean against objects; profuse salivation; food material impacted in the cheek of the affected side; drooping ear, deviated muzzle, flaccid lip on the affected side; lowered eyelid on the affected side; weakness along affected side of body;

Diagnosis can be difficult, too, as your vet will also have to consider such problems as pregnancy toxaemia in heavily pregnant ewes during the last four weeks of pregnancy; peripheral vestibular lesions, or middle ear infections; brain abscesses; or gid (or coenurosis, a tapeworm cyst in the brain).

Finally laying the blame with listeriosis will be based upon a thorough veterinary examination once these other issues have been ruled out.

Care should also be taken when silage-making and the use of additives which kill the bacterium are recommended. When making clamp silage, make sure the grass is rolled continuously and well sheeted to prevent air ingress. Use a block cutter for a clean finish on the silage face and try to cut across a narrow band of the silage face.

For big bale silage it is important that any punctures on the outer plastic skin are immediately sealed and that the store of big bales should be fenced against damage by farm stock and vermin, and vermin control is imperative.

Treatment - early detection of illness; prompt aggressive antibiotic treatment prescribed by the veterinary practitioner; high doses of antibioticoral propylene glycol to prevent development of a severe energy deficit; fresh palatable foods and clean water must always be available; atopical antibiotic eye ointment should be applied twice daily;

Prevention/control - discard spoiled silage (or feed to cattle); clean feed troughs daily; avoid soil/manure contamination of feed troughs from tractor wheels etc; discard refusals; clean water troughs regularly;