an epidemiological study of listeriosis in dairy cattle

24.4% (10/41) L. innocua and 9.7% (4/41) L. seeligeri. No Listeria were isolated from
the remaining 24.4% (10/41).
The proportion of animals shedding Listeria spp. and L. monocytogenes
varied between 1.9% to 52.8% and 0 to 33.3% respectively. The highest proportion of
cows excreting Listeria spp. and L. monocytogenes was in November and March
respectively (Figure 6. 4). Grass silage was introduced 13 days before the October visit
but the proportion of animals shedding Listeria spp. remained low. The cattle were
housed 26 days before the November visit and by this time the proportion of animals
shedding Listeria spp. had increased to 52.8% (28/53). However the proportion of
animals shedding L. monocytogenes remained low throughout the winter months.
(Table 6. 1). The proportion of animals excreting L. monocytogenes in March was
significantly higher (P