  The Cattle Tracing System database is an online recording system for cattle
births, deaths and between--herd movements in the United Kingdom. Although it
has been thoroughly examined, the most recently reported movement analysis is
from 2009. This article uses the database to construct weighted directed
monthly movement networks for two distinct periods of time, 2004--2006 and
2015--2017, to quantify by how much the underlying structure of the network has
changed. Substantial changes in network structure may influence policy--makers
directly or may influence models built upon the network data, and these in turn
could impact policy--makers and their assessment of risk. Four general network
measures are used (total number of nodes with movements, movements, births and
deaths), in conjunction with network metrics to describe each monthly network.
Two updates of the database were examined to determine by how much the movement
data stored for a particular time period had been cleansed between updates.
Statistical models show that there is a statistically significant effect of the
time period (2004--2006 vs 2015--2017) in the values of all network measures
and six of nine network metrics. Changes in the sizes of both the Giant and
Weakly Strongly Connected components predict reductions in the upper and lower
bounds of the maximum epidemic size. Examination of the updates of the database
show that there are differences in records between updates and therefore
evidence of historical data changing between updates. Accurate modelling of
disease spread through a network requires representative descriptions of the
network. The authors recommend that where possible the most recent available
data always be used for network modelling and that methods of network
prediction be examined to mitigate for the time required for data to become
available.
