an epidemiological study of listeriosis in dairy cattle

Some important farming practices were identified as risk factors for clinical
listeriosis. These were mainly forage and forage related practices (Chapter 3 and 4).
This study demonstrated that the methods of making and feeding grass silage are an
important component of the association between silage feeding and Listeriosis. Clinical
Listeriosis was associated with the time and stage of harvest (number of cuts made to
grass for grass silage), soil contamination (presence of mole hills in the fields, control of
moles, use of mower conditioner), type of harvesters (mower conditioner), wilting,
storage of grass silage (clamp, big bale silage and storage of big bales outside
uncovered). These factors are also believed to be involved in the production of good
quality silage. These have been discussed in the relevant chapters.
As important as silage quality are the method or methods of feeding silage.
Some clinical forms of Listeriosis (encephalitis, iritis) have been attributed to physical
injuries of mucosal membranes such as buccal or conjunctival membranes caused by
rough forages. In addition to the factors stated above methods of feeding grass silage
were also associated with disease. These were the feeding of grass silage both in ring
feeders and ad libitum feeding during the indoor or outdoor period.
This study has also established an association between maize silage feeding and
disease. Although we gathered information about the preparation of maize silage and its
quality, we failed to identify risk factors in the preparation of maize silage. The methods
of maize silage feeding were significantly associated with disease; maize silage feeding
ad libitum, in ring feeders or in a complete diet during the indoor or outdoor period.
Maize silage feeding is an increasing practice in the UK. There is a need for more
research to establish the factor or factors that influence its quality.
In the second part of the study a longitudinal study, employing bacteriological,
serological and molecular techniques, was carried out. This study demonstrated that a
large proportion of animals excrete L. monocytogenes during the winter months without
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