(Photo Credit: University of Tennessee)Pig bodies have been used as analogues for human corpses in forensic science for decades. Since human remains are so difficult to obtain – and so tightly regulated – the pigs have been considered biologically similar enough to provide a good estimate of the dynamics of death in humans.

Pigs’ decomposition in the wilds and underwater have been measured minutely and compared against that of humans, and live pigs have even been shot in the head to gauge the degree of blood backspatter toward a firearm.

But the decomposition forensic models that have been used in courts worldwide will have to be reconsidered, according to an ambitious new series of studies by a team of researchers at the famed “Body Farm” run by the University of Tennessee.

Human decomposition is much more variable than pigs or rabbits, they reportedly found.

Three papers have been presented to the American Academy of Forensic Science, and three more are being prepared for submission to The Journal of Forensic Science.

“This research provides guidance to lawyers and judges concerning the admissibility of testimony by anthropologists and entomologists,” said Dawnie Steadman, the principal investigator, and director of UT’s Forensic Anthropology Center. “Now (they) may be asked in court which studies they used to base their estimate of postmortem interval, and if they are based on nonhuman studies, their testimony could be challenged.”

Five specimens of each species were placed at the Body Farm over three seasons: spring, summer and winter. Decomposition patterns and rates of decay – including the infestation by insects and scavenging by bigger species – were observed and recorded.

In the spring, all the decomposition was similar for weeks. But at the 25-day mark, insect activity really picked up – and the pigs started to skeletonize much faster than the humans. Rabbits, meanwhile, appeared to decay slower – until maggot activity picked up, and significantly decomposed within just 24 hours, according to a statement by the school.

READ MORE: 'Body Farm' Finds Microbial Ecosystems Could Pinpoint Time of Death

The second trial was in the summer. Pigs consistently decomposed quicker than both the rabbits and humans. Maggots not only worked faster, but also consumed more of, the pigs rather than the humans.

The winter trial showed no insect activity for 100 days. But scavenger activity continued unabated – and zeroed in on the human remains. The raccoons, birds and skunks overwhelmingly preferred the human remains above the other carcasses, the scientists noted.

“This strongly indicates a preference for the humans over the other species,” the study finds. “With one notable exception, human scavenging begins on the limbs, while the snout and abdomen are the initial preferred scavenging sites on pigs.”

Decomposition work with pigs, however, continues apace at other institutions. Last month, a team from Simon Fraser University working in coastal waters off British Columbia found that porcine carcasses in deeper, more-oxygen-rich water decomposed faster.

One of the Tennessee authors to work on the latest group of trials is Jennifer DeBruyn, a microbial ecologist who was profiled by Forensic Magazine last year for her in-depth studies of the breakdown of the gut of human corpses.