Descriptive analysis of pig production pyramids in Great Britain, 2016 – 2018

Key findings

Between 2016 and 2018, pig holdings registered to APHA under PRIMO represented 1.3% of the pig
holdings that actively moved pigs in Great Britain. Over this period, we identified 19 pyramids within which
pigs flow from breeding (Tiers 1 and 2) to finishing (Tier 4) units and that were registered to APHA. We also
found 18 production pyramids that only included PRIMO-approved production units (Tier 3) and finishing
units (Tier 4) but did not show records of receiving pigs from PRIMO-approved breeding holdings. These
production pyramids did not show any records of unique identifier and were therefore considered as not
registered (NR) to APHA under PRIMO. Altogether, 516 and 67 holdings were involved in moving pigs within
registered and NR pyramids, respectively.

On average, 177,000 non-slaughter pigs moved per week between holdings in GB, among which only 9%
moved within pyramids when considering the most inclusive definition of pyramids (Tiers 1 to 4, including NR
pyramids). Overall, 21%, 33% and 66% of all non-slaughter pigs moving within pyramids travelled for <10km,
<20km and <50km, respectively. In contrasts, pigs moving to slaughter from an holding belonging to a
pyramid travelled for <10km, <20km and <50km in 3%, 7% and 28% of the time, respectively.
Registered pyramids showed a high level of interconnectivity and were not isolated from the rest of the
British pig industry. Notably, pigs were reported moving between 13 of the 19 registered pyramids
throughout the study period, forming a large network including 91% of all holdings involved in moving pigs
within registered pyramids. Pigs were moving between pyramids through 124 holdings, among which only 35
were found critical for the cohesion of the network.

In the situation where an incursion of an infectious disease occurs and movement restrictions over the all
industry are enforced to mitigate its spread, the least restrictive strategy (that is allowing the most number of
movements) among all scenarios considered would be based on pyramids being defined as involving holdings
from all tiers (Tiers 1 to 4) and included NR pyramids. In this strategy, movement licences would then be
granted for pigs travelling both within pyramids and for <50km of distance. This derogation strategy would
allow the flow of ~65% of all pigs within pyramids, particularly preserving movements between Tiers 3 and 4
holdings. Yet, over the total number of pigs moving within GB, this strategy would only allow 6% of the pigs to
move, irrespective of the length of time within which movement restrictions are enforced.
Determining which finishing units belonged to the Tier 4 of pyramids was challenging and may introduce
some uncertainties in our interpretations. Notably, only 14% of the 1954 non-approved holdings receiving
pigs from PRIMO-approved farms met our definition critera for being included as part of a pyramid.
Furthermore, allocating holdings in the Tiers 3 and 4 of specific pyramids using movement records alone was
difficult. Efforts to improve registration and database structure should be made if pyramids are to be used for
modulating disease control responses.

Policy implications

This study highlights that the structure of the pig industry in GB is more complex than the theoretical
top-to-bottom structure of vertically integrated pig production companies. There was a high level of
interconnection between pyramids that is misaligned with their use as a basis for compartmentalisation
during outbreak response. Furthermore, movement regulations based on pyramids may not be as effective as
expected in order to prevent and control the spread of infectious disease or protect the industry as a whole.
Efforts to improve registration and database structure are recommended if pyramids are to be used for
modulating control responses against outbreaks of pig infectious diseases.