An automatic milking system (AMS) uses a robot to attach the teatcups
and can
be continuously available for cows to present themselves to be milked with
minimal
human intervention. Milking in an AMS is therefore a continuous rather
than a batch
process, and the conventional practice of cleaning a milking system after
each batch
of cows has been milked is not applicable.
Milk flow through an AMS is different in scale and in temporal distribution
from
that in a conventional system. These differences in flow patterns may be
significant
for hygiene. It has been suggested by Verheij (1992), for example, that
milk will flush
away much of the residue of the previous milking and that microbial growth
will be
retarded because of the bacteriostatic properties of fresh milk. Ordolff
& Bölling
(1992) reported experiments in which batches of milk were passed through
a milking
installation that was said to simulate an AMS. Their main conclusion was
that milk
residues left in the system for up to 60 min did not increase the bacterial
contamination of the next batch of milk. However, the practical relevance
of this
conclusion is not clear because the design of the simulated AMS was not
specified, so
it can not be compared to a practical AMS. Moreover, mixtures of fresh
and UHT
milk were used, with unknown consequences. The purpose of the experiment
reported in this paper was to strengthen the evidence on which to base
recommendations for effective cleaning procedures for AMS.
The bacterial count of milk that had been passed through a system was
used as
the indicator of the cleanliness of the system. It was apparent from previous
work by
Ordolff & Bölling (1992) that this would produce results that
varied widely. The
experiment was therefore designed to be as simple as possible. In particular,
a simple,
easily defined laboratory rig was used rather than an AMS.