an epidemiological study of listeriosis in dairy cattle

(ii) Cases in milking cows: Farms reporting at least one case of Listeriosis in milking
cows.
(iii) Cases in winter months: This includes only those farmers reporting cases of
Listeriosis in winter months.
(iv) Cases of silage eye (iritis): Farms reporting silage eye as a clinical sign.
(v) Cases of nervous signs: Farms which reported cases of listeriosis showing nervous
signs.
3. 2. 3. Predictor variables:
The five groups of predictor variables were herd size, feeding practices, forage
making, housing and general management. These included binary, categorical and
continuous variables. Each group of predictor variables had subsets of variables that are
dealt with under the related headings. When continuous variables were categorised the
cut off points for each categories were set according to known biological influences e.
g. pH, number of cuts and wilting.
(i) Herd size:
The herd size reported in July 1994 and June 1995 was used as a categorical
variable with 3 herd sizes:-the number of animals on each farm less than or 50, 51-100,
and greater than 100 animals.
(ii) Feeding practices:
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