an epidemiological study of listeriosis in dairy cattle

A contradictory finding was made about the use of straw bedding in cubicles.
This was associated with an increased risk of disease in univariate analysis and in model
1. However, it was associated with a decreased risk of reporting Listeriosis in milking
cows in model 2. It may be speculated that the majority of farmers may have had better
management system or cubicle housing system on those farms who fed only maize
silage.
There was a negative association between grazing sheep on the same field as
dairy cattle and the risk of disease. This may have been due to better pasture
management. It may be possible that sheep grazed on the pasture during winter months
when animals were housed. Even if sheep excreted the organism during this period, by
the time that dairy cattle were turned out sheep had long been moved to other fields and
the organism may have decreased significantly in number. It is known that L.
monocytogenes survives in sheep faeces for 3 months (reviewed by Radostits and
others 1994)
The analysis of the questionnaire data has enabled us to identify some important
risk factors for clinical Listeriosis in dairy cattle at farm level. These factors are mainly
related to the infection pressure of the organism. The study has shown the importance of
proper silage making, preservation and methods of feeding. It has also suggested the
importance of better management at housing (e.g. use of bedding, dung disposal) and
some general management factors (e.g. control of moles in the fields, separation of sick
animals). However to reach a better understanding of the disease L. monocytogenes
infection should also be investigated at individual animal level. The next two chapters
consider the infection in dairy cattle and its possible risk factors.