Postmortems are routinely done on the feedlot. However, in order guard against misdiagnosis, it's important to understand the process of autolysis and how it can change tissues over time. There is always a challenge of differentiating autolysis from a real lesion.
Autolysis starts as soon as the animal dies. Bruce W. Brodersen, DVM, PhD, University of Nebraska-Lincoln says due to the microbial flora, the gastrointestinal tract is the quickest to undergo autolysis. "Within a matter of minutes, autolysis begins and within a few hours, epithelial cells will have sloughed off the mucosa," he says. "Sloughing begins at the tips of villi within minutes after death and proceeds toward the mucosal crypts. Gravitation of blood to dependent areas begins within minutes and can give the appearance of congestion and may be misinterpreted as inflammation. This is a common cause of a misdiagnosis of enteritis."
Speaking at the 2011 Annual Western Veterinary Conference, Brodersen says gravitation of blood to other organs such as lungs, liver, kidney, and spleen is common and should be taken into consideration when observing changes in color. "Odd or peculiar color patterns can also be the result of blood pooling or blood being displaced due to pressure by adjacent structures or organs," he explains. "For example, as the rumen distends due to gas production post mortem, blood may be squeezed out of surrounding organs, leaving a pale color."
In more advanced stages of autolysis, hemolysis leaves free hemoglobin to diffuse into adjacent tissues. This results in a rather monochromatic red color of all the tissues. This is hemoglobin imbibition and the best example is seen in aborted fetuses which have been expelled several days after death in utero. Other changes occur as a result of endogenous enzymes released from dead cells and from bacteria. "Saprophytic bacteria spread rapidly and will complicate isolation of pure cultures of bacterial pathogens," Brodersen adds. "Histologic examination of autolytic tissues often reveals numerous large bacilli randomly and evenly disseminated throughout the sections."