Pig carcass decomposition dynamics: Insights into carcass disposal for emergency animal disease management

Australia is free from many economically devastating emergency animal diseases (EADs) that threaten livestock production in neighbouring countries. In Australia, an important consideration for EAD control is managing susceptible feral animal populations, especially in remote and inaccessible areas where carcass disposal poses considerable logistical challenges. One proposed solution is to utilise natural decomposition above ground through the 'destroy and let lie' (D&LL) method, relying on post-mortem changes in carcass temperature and pH to inactivate the EAD agent. We investigated temperature and pH changes in pig carcasses from death until end-stage decomposition at two locations in Queensland to gain insights into how carcasses left in situ decompose under Australian conditions. Using regression modelling, we identified days since humane killing, air temperature, rainfall, relative humidity, anatomical site and study location as significant predictors of carcass pH and temperature. Although the observed carcass pH and temperature conditions did not meet African swine fever virus (ASFV) inactivation thresholds, foot-and-mouth disease virus (FMDV) was likely to be inactivated in the thoracic cavity, superficial and deep skeletal muscle and abdominal cavity of most carcasses. However, FMDV inactivation thresholds were not reached in bone marrow and brain. This suggests that these carcasses may potentially remain infectious with ASFV and FMDV in situ under the experimental conditions encountered, based on the inactivation thresholds selected. Despite this, culling large portions of a feral pig population, in conjunction with D&LL disposal approach, may still support disease control imperatives during an EAD response by reducing live pig numbers and disease transmission.