an epidemiological study of listeriosis in dairy cattle

monocytogenes. By April the proportion of cows excreting L. monocytogenes had
fallen whereas the proportion excreting L. innocua was similar to that seen in March.
Grass silage feeding ended 20 days before the April sampling and winter housing also
ended 9 days before this visit (Table 6. 8). This farm had bought in silage three weeks
before the 8th visit (17/3/1997).
b) Environmental samples:
Listeria was not isolated from soil but L. innocua was isolated from water, grass
and bedding and L. monocytogenes was also isolated from grass, silage, bedding and
milk. Milk samples collected between October and March were persistently positive for
L. monocytogenes. L. seeligeri was isolated from bedding materials on one occasion.
(Table 6. 14). Concentrate bulk feed stored in a shed was sampled on one occasion and
L. monocytogenes was isolated from it.
Figure 6. 5. The monthly faecal excretion of Listeria spp. and L. monocytogenes on
Farm D.
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