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Free keywords:
network analysis; pig trade network; animal movements; Germany
Abstract:
Transport of live animals is a major risk factor in the spread of infectious diseases between
holdings. The present study analysed the pork supply chain of a producer community
in Northern Germany. The structure of trade networks can be characterised by carrying
out a network analysis. To identify holdings with a central position in this directed network
of pig production, several parameters describing these properties were measured
(in-degree, out-degree, ingoing and outgoing infection chain, betweenness centrality and
ingoing and outgoing closeness centrality). To obtain the importance of the different holding
types (multiplier, farrowing farms, finishing farms and farrow-to-finishing farms) within
the pyramidal structure of the pork supply chain, centrality parameters were calculated
for the entire network as well as for the individual holding types. Using these centrality
parameters, two types of holdings could be identified. In the network studied, finishing
and farrow-to-finishing farms were more likely to be infected due to the high number of
ingoing trade contacts. Due to the high number of outgoing trade contacts multipliers and
farrowing farms had an increased risk to spread a disease to other holdings. However, the
results of the centrality parameters degree and infection chain were not always consistent,
such that the indirect trade contacts should be taken into consideration to understand
the real importance of a holding in spreading or contracting an infection. Furthermore, all
calculated parameters showed a highly right-skewed distribution. Networks with such a
degree distribution are considered to be highly resistant concerning the random removal
of nodes. But by strategic removal of the most central holdings, e.g. by trade restrictions
or selective vaccination or culling, the network structure can be changed efficiently and
thus decompose into fragments. Such a fragmentation of the trade networks is of particular
importance from an epidemiological perspective.
