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an epidemiological study of listeriosis in dairy cattle

an epidemiological study of listeriosis in dairy cattle

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entered <strong>an</strong>d left the herd over the <strong>study</strong> period, so that only 78 (62.9%) <strong>an</strong>imals were<br />

exam<strong>in</strong>ed at all visits <strong>an</strong>d the rest (37.1%) were either removed from or <strong>in</strong>cluded <strong>in</strong> the<br />

herd at different times dur<strong>in</strong>g the survey (Table 6. 5). All 78 milk<strong>in</strong>g cows shed L.<br />

monocytogenes at some stage dur<strong>in</strong>g the <strong>study</strong>.<br />

The proportion <strong>of</strong> milk<strong>in</strong>g cows excret<strong>in</strong>g Listeria spp. varied between 1% <strong>in</strong><br />

September to 96.5% <strong>in</strong> March (Figure 6. 2). The highest frequencies <strong>of</strong> excretion were<br />

observed between November <strong>an</strong>d April <strong>in</strong>clusive. A similar pattern <strong>of</strong> excretion was<br />

observed for L. monocytogenes (1% <strong>in</strong> September <strong>an</strong>d 90% <strong>in</strong> February). The<br />

proportion <strong>of</strong> <strong>an</strong>imals excret<strong>in</strong>g L. <strong>in</strong>nocua gradually <strong>in</strong>creased <strong>an</strong>d reached the highest<br />

level <strong>in</strong> December (Figure 6. 2).<br />

The difference between the months was statistically signific<strong>an</strong>t (P

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