an epidemiological study of listeriosis in dairy cattle

a) Type of forages fed to animals: Farmers were asked to state whether they fed any of
the following forages; grass silage, maize silage, hay, feed straw and root crops. These
variables were treated as binary variables except for straw and root crops which were
first treated as binary then categorised according to type (barley, wheat, potatoes, sugar
beet etc.).
b) Source of forages: The farmers were asked about the source of their forages. Three
options were provided; home-made, purchased and other sources. These were treated as
binary variables.
c) Month of feeding forages: To assess the relationship between the duration of feeding
and Listeriosis farmers were asked to state the month in which forage feeding started
and stopped. The duration of feeding forages was used as categorical variable with 4
levels: - less than 6 months, 6 months, more than 6 months and all year around.
d) Methods of feeding forages: These were divided into those used during the outdoor
period and indoor period. A list of feeding methods was given on the questionnaire.
This included ad libitum, on the ground, at the clamp face, in hay racks, off the field, in
ring feeders etc. (Appendix 1). These variables were treated as binary variables for each
forage.
iii) Making forage crops:
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