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Research article - Peer-reviewed, 2003

Survival of Listeria monocytogenes in wilted and additive-treated grass silage

Pauly TM, Tham WA


Grass was field-dried to 3 different dry matter (DM) levels (200, 430 and 540 g/kg) and inoculated with 10(6)-10(7) Cfu/g of a Listeria monocytogenes strain sharing a phagovar occasionally involved in food-borne outbreaks of listeriosis. Formic acid (3 ml/kg) or lactic acid bacteria (8.10(5)/g) with cellulolytic enzymes were applied only to forages with low and intermediate DM levels. Forages were ensiled in laboratory silos (1700 ml) and were stored at 25degreesC for 30 or 90 days. After 90 days of storage, L. monocytogenes could not be detected in any silo, except one with the high dry matter grass without additive. After 30 days of storage, between 102 and 106 cfu L. monocytogenes/g silage were isolated from the untreated silages. Increasing the DM content from 200 to 540 g/kg did not reduce listeria counts possibly because of the lower production of fermentation acids (higher pH). In silages treated with additives, counts of L. monocytogenes were always lower than in silages without additive. In wet silages (DM 200 g/kg) both additives were effective, but in the wilted silages (DM 430 g/kg) only the bacterial additive reduced listeria counts below detection level. Listeria counts were highly correlated to silage pH (r = 0.92), the concentration of lactic acid (r = -0.80) and the pooled amount of undissociated acids (r = -0.83)

Published in

Acta Veterinaria Scandinavica
2003, volume: 44, number: 1-2, pages: 73-86

Authors' information

Pauly, Thomas
Swedish University of Agricultural Sciences, Department of Animal Nutrition and Management
Tham, Wilhelm
Swedish University of Agricultural Sciences, Department of Biomedical Science and Veterinary Public Health

UKÄ Subject classification

Veterinary Science
Food Science
Animal and Dairy Science

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