Scoring of Decomposition: A Proposed Amendment to the Method When Using a Pig Model for Human Studies

Abstract

Decomposition studies often use pigs as proxies for human cadavers. However, differences in decomposition sequences/rates relative to humans have not been scientifically examined. Descriptions of five main decomposition stages (humans) were developed and refined by Galloway and later by Megyesi. However, whether these changes/processes are alike in pigs is unclear. Any differences can have significant effects when pig models are used for human PMI estimation. This study compared human decomposition models to the changes observed in pigs. Twenty pigs (50-90 kg) were decomposed over five months and decompositional features recorded. Total body scores (TBS) were calculated. Significant differences were observed during early decomposition between pigs and humans. An amended scoring system to be used in future studies was developed. Standards for PMI estimation derived from porcine models may not directly apply to humans and may need adjustment. Porcine models, however, remain valuable to study variables influencing decomposition.

A field study to evaluate PMI estimation methods for advanced decomposition stages

“…Today, pigs are largely accepted as a reasonable model in forensic sciences and are frequently used for decomposition studies due to their similar physical and biochemical preconditions to humans [37,39]. Although some variations to human decomposition have been reported [11,40], pigs generally depict similar morphological changes [41]. This is also supported by the results of this study.…”

Differential Decomposition Among Pig, Rabbit, and Human Remains

“…Use of consistent methods of evaluation is needed in order for research data to be comparable to other studies and must be accurately applied to all specimens. Keough et al have proposed a modification of the TBS system for pigs in South African environments, but currently, there is no such modification available for rabbits. It should also be noted that the differences in decomposition rate observed in rabbits cannot be simply attributed to the fact that the rabbits were caged while the pig and humans were not.…”

Testing the Use of Pigs as Human Proxies in Decomposition Studies

“…Limited scoring options may reduce or eliminate the resolution necessary to highlight divergence in gross change. Keogh et al used the Megyesi et al TBS to define the typical trajectory of human decomposition and compared this to observations made within a sample of 20 pig carrion. The authors concluded that the gross changes observed between the two groups were sufficiently different to warrant a separate scoring system for pig carrion.…”

“…The initial samples of pigs appear more homogenous and humans more varied, but the pigs tend to have a greater coefficient of variation (Table , Figs ), particularly after a TBS of 25. This may partly be due to the fact that the TBS model was created for humans and does not work as well with pigs . Furthermore, while a pig sample may present as “healthy” and homogeneous in gross examination, animals reared for consumption are not subject to regular health assessment and should not be assumed to be homogeneously “healthy” at the time of death.…”