Lawsonia intracellularis and Stalosan F April 2001 Lawsonia intracellularis is a bacteria. During stressful periodes can it make the pigs suffer from especially diarrhoea and enteritis. Reduced growth, benefit of feed and condition are effects, the farmer is not always aware of. Never-the-less a lot of welfare and money is lost because of this bacteria. Eliminating Lawsonia intracellularis from the farms have been considered as practically impossible. Guidelines for that tell the farmer to medicate the breeding animals for 14 days, move the animals to newly cleaned and disinfected and/or fumigated sties. After this the animals should be medicated again for 14 days. No new animals can be introduced from other farms because they will bring the bacteria into the sties again. - The bacteria can survive 14 days on things used in the sties (boots, clothing, broom, shovel, .). These should be cleaned thoroughly or removed permanently. Attention to and from the staff is also essential. The bacteria is easily spread after just one oversight. Rhodents, birds and even insects can probably also spread the bacteria. Stalosan F was spread in 4 farms for 3 consecutive days and then once a week (50 g/m ² ) for 3 month. In addition to this Stalosan F was put on suspiciously looking faeces (diarrhoea). To find a possible effect floor-samples were taken at the start before Stalosan F was used the first time and then after using Stalosan F for 3 month. Test-results, floor-samples Brinkmann, Farm 1 Sæderup, Farm 2 Drost, Farm 3 Jørgensen, Farm 4 Total Before Stalosan F Lawsonia No Lawsonia 6 1 9 6 1 7 4 22 20 36 After Stalosan F Lawsonia No Lawsonia 0 10 0 13 0 10 0 29* 0 62 *One sample from new-bought gilts was positive with Lawsonia intracellularis one month earlier, but all were negative at the end of the trial. Stalosan F seems to have some effect. Theese 4 farms paid a lot of attention to Lawsonia intracellularis and was chosen to this trial by their vet. Torben Svendsen and Leon Lau, (certificate holders in swine diseases). I visited the farms at trial-start, once monthly till the floor-samples were taken after 3 month. All the samples were PCR-tested, wich is a very sensitive and very specific test. DVM Anna Ibsen