Post mortem bruising in dogs and cats - An experimental cadaveric study

Forensic veterinary pathology is an emerging discipline which plays an essential role in the investigations regarding animal abuse and unlawful killing. The task is made difficult in veterinary pathology as the discipline concerns a vast multitude of species represented by companion animals, exotics, farmed livestock and wildlife: extrapolating results from one species to another may lead to unreliable outcomes. Aims of the present work are to characterise the formation of post-mortem bruising in cats and dogs, and to differentiate the ante- from post-mortem gross lesions. Fifty-eight deceased animals (without pre-mortem bruising) and nine control animals (with intra-vitam head trauma) were included in the study: 36 dogs (53.7%) and 31 cats (46.3%), of which 58 represented the experimental group and 9 the positive control group (5 dogs and 4 cats). The study population was further characterised according to species, sex, age category, body weight and preservation method. Forty-three (64.2%) cadavers were immediately frozen after death and 24 (35.8%) were preserved at 4°C for 1-96 h before the experimental procedure. The cadavers were placed in a prone position and a plastic tube (150 cm in length) was placed perpendicularly upon the frontal region of the animal's head. A commercially available hollow steel pétanque (boules) ball, weighing 660 g and measuring 73 mm in diameter, was released from the upper end of the tube and allowed to fall freely under the influence of gravity until striking the frontal region of the head. The impact produced a standardized blunt-force impact with an approximate theoretical kinetic energy of 9.7 J. The frontal region of the skull was then skinned and photographed to document the presence or absence of any associated changes and morphological features were recorded, when noted. Statistical analysis was performed to evaluate the association among variables. Overall, 19 of the 67 animals (28.4%) developed a grossly visible post-mortem contusion. Although post-mortem bruising could be experimentally reproduced, these lesions consistently differed from ante-mortem contusions with regard to their anatomical distribution, extent and associated gross pathological findings. The present findings provide practical macroscopic criteria that may assist forensic veterinary pathologists in distinguishing post-mortem pseudo-bruising from genuine ante-mortem contusions during forensic necropsy. Furthermore, the study contributes novel experimental data to an area where objective veterinary evidence is currently scarce, supporting a more reliable interpretation of blunt-force injuries in forensic investigations.