an epidemiological study of listeriosis in dairy cattle

Listeriosis in others
beef cattle
sheep
4. 2. 1. Model Building:
Vaccine
Leptospirosis
Lung worm
mole hills
in grass silage field
controlling moles
It was not possible to fit all the selected variables in a single model. This caused
us to develop first a preliminary model that included all the major variables like herd
size, types of forages fed to animals, housing, dung disposal variables and general
management as binary variables. The effects of more qualitative aspects of each
variable e.g. method of feeding forage, silage analysis that were statistically significant
in the preliminary model were then investigated in detail by including more explanatory
variables in other models. Finally variables which reduced the statistical power of the
model because of large numbers of missing values, e.g. herd size (84 observations), or
the variables which had strong effect on the model, e.g. cases in beef cattle (reported by
14 farms), were excluded from the data set.
4. 3. Results:
(i) Preliminary Model:
Using the overall cases reported in dairy cattle as an outcome variable a model
was developed to include the variables listed below, namely feeding forages, housing,
dung disposal, general management. Grass silage feeding was not included at this stage
because those who did not feed grass silage did not report any cases of Listeriosis.
The list of variables used in the preliminary model is as follows: