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an epidemiological study of listeriosis in dairy cattle

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visualised over a UV-Tr<strong>an</strong>sillum<strong>in</strong>ator. Results were recorded on Polaroid type 665<br />

<strong>in</strong>st<strong>an</strong>t positive/negative film (Polaroid, Hertfordshire, UK).<br />

6. 2. 8. Data <strong>an</strong>alysis:<br />

In estimat<strong>in</strong>g the effect <strong>of</strong> silage feed<strong>in</strong>g <strong>an</strong>d hous<strong>in</strong>g on the overall excretion <strong>of</strong><br />

Listeria spp. <strong>an</strong>d L. monocytogenes, all <strong>an</strong>imals exam<strong>in</strong>ed (i.e. <strong>an</strong>imals left or entered<br />

the milk<strong>in</strong>g herd <strong>in</strong>cluded) before, dur<strong>in</strong>g <strong>an</strong>d after silage feed<strong>in</strong>g <strong>an</strong>d hous<strong>in</strong>g were<br />

taken <strong>in</strong>to account <strong>an</strong>d then the proportions <strong>of</strong> <strong>an</strong>imals positive for the org<strong>an</strong>ism before,<br />

dur<strong>in</strong>g <strong>an</strong>d after hous<strong>in</strong>g <strong>an</strong>d silage feed<strong>in</strong>g were estimated <strong>an</strong>d compared.<br />

All data were entered onto a database (Micros<strong>of</strong>t Access 2, Simpson 1994) <strong>an</strong>d<br />

<strong>an</strong>alysed us<strong>in</strong>g Epi-<strong>in</strong>fo version 6 (De<strong>an</strong> <strong>an</strong>d others 1994). A Yates corrected chi<br />

squared test was used to compare the differences between proportions. A Kruskal-<br />

Wallis test was used to compare the differences between medi<strong>an</strong> values (De<strong>an</strong> <strong>an</strong>d<br />

others 1994). A probability <strong>of</strong> P< 0.05 was accepted as statistically signific<strong>an</strong>t.<br />

6. 3. Results:<br />

6. 3. 1. Bacteriology :<br />

Farm A:<br />

a) Faecal samples:<br />

A total <strong>of</strong> 124 milk<strong>in</strong>g cows were exam<strong>in</strong>ed on this farm. Of these, 72.6%<br />

(90/124) shed L. monocytogenes <strong>an</strong>d 1.6% (2/124) other species <strong>of</strong> Listeria. Animals<br />

170

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