an epidemiological study of listeriosis in dairy cattle
an epidemiological study of listeriosis in dairy cattle
an epidemiological study of listeriosis in dairy cattle
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caused damage on the conjunctival membr<strong>an</strong>es allow<strong>in</strong>g L. monocytogenes to penetrate<br />
these membr<strong>an</strong>es. The latter assumption may f<strong>in</strong>d some support from the association<br />
found between outdoor ad libitum feed<strong>in</strong>g grass silage <strong>an</strong>d <strong>an</strong> <strong>in</strong>creased risk <strong>of</strong><br />
report<strong>in</strong>g silage eye <strong>in</strong> this <strong>study</strong>. Another expl<strong>an</strong>ation for the effect <strong>of</strong> outdoor ad<br />
libitum feed<strong>in</strong>g may be that the quality <strong>of</strong> silage would be poorer due to exposure to air<br />
<strong>an</strong>d unfavourable weather conditions therefore the qu<strong>an</strong>tity <strong>of</strong> L. monocytogenes would<br />
be much higher th<strong>an</strong> at the beg<strong>in</strong>n<strong>in</strong>g <strong>of</strong> silage feed<strong>in</strong>g.<br />
Maize silage feed<strong>in</strong>g <strong>in</strong> a complete diet when <strong>an</strong>imals were housed was<br />
associated with <strong>an</strong> <strong>in</strong>creased risk <strong>of</strong> report<strong>in</strong>g Listeriosis <strong>in</strong> milk<strong>in</strong>g cows. This may<br />
have been due to <strong>an</strong> <strong>in</strong>crease <strong>in</strong> the numbers <strong>of</strong> the org<strong>an</strong>ism <strong>in</strong> the diet because a<br />
complete diet conta<strong>in</strong>s several forages <strong>in</strong>clud<strong>in</strong>g hay, straw, grass silage.<br />
It is known that spread<strong>in</strong>g <strong>an</strong>imal waste on fields plays <strong>an</strong> import<strong>an</strong>t role <strong>in</strong><br />
environmental contam<strong>in</strong>ation with L. monocytogenes <strong>an</strong>d poses great a health hazard to<br />
<strong>an</strong>imals <strong>an</strong>d hum<strong>an</strong>s (Wray 1975, Jones 1980, Pell 1997). In this <strong>study</strong> there was a<br />
statistically signific<strong>an</strong>t association between not stor<strong>in</strong>g m<strong>an</strong>ure <strong>an</strong>d <strong>an</strong> <strong>in</strong>creased risk <strong>of</strong><br />
disease (overall cases <strong>an</strong>d cases <strong>in</strong> milk<strong>in</strong>g cows). These farms may have spread m<strong>an</strong>ure<br />
on the fields where <strong>an</strong>imals were graz<strong>in</strong>g or grass <strong>an</strong>d maize silage, hay or straw was<br />
made. This variable was also <strong>in</strong>cluded <strong>in</strong> all the multivariate models but it was not<br />
signific<strong>an</strong>tly associated with <strong>an</strong>y <strong>of</strong> the outcome variables.<br />
An association was found between the use <strong>of</strong> big bale straw as a bedd<strong>in</strong>g<br />
material <strong>an</strong>d a decreased risk <strong>of</strong> report<strong>in</strong>g cases <strong>of</strong> silage eye. This was only signific<strong>an</strong>t<br />
<strong>in</strong> the models 2 where the <strong>an</strong>alysis was restricted to those who fed maize silage. It may<br />
be that bal<strong>in</strong>g reduced the exposure <strong>of</strong> straw to unfavourable weather conditions or<br />
extra contam<strong>in</strong>ation with L. monocytogenes orig<strong>in</strong>at<strong>in</strong>g from other sources, result<strong>in</strong>g <strong>in</strong><br />
the straw be<strong>in</strong>g free <strong>of</strong> L. monocytogenes or harbour<strong>in</strong>g very low numbers <strong>of</strong> the<br />
org<strong>an</strong>ism.
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