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To complete an effective necropsy, specific and consistent protocols (procedure, sampling, documentation) should be followed. The optimal time to perform a necropsy is as soon as possible after the animal's death. Depending on environmental conditions, changes in tissues occur in minutes after an animal has expired. It is important, for an accurate diagnosis, to take appropriate tissue samples for culture and/or microscopic examination in a timely fashion. If a necropsy cannot be performed immediately, the animal should be placed in a cooler (for up to two days post‐death). Tissue integrity and most pathogens and toxins are stable during that time, although overgrowth of postmortem bacteria becomes a problem. For any longer time window, freezing the carcass is warranted.

Any animal that dies should be examined to the best of one's time and ability; however, a necropsy performed specifically for sample collection can be much shorter (for example, collecting gastrointestinal (GI) samples in a dog with diarrhea to confirm or exclude parvovirus). Here are a few important considerations before performing a necropsy:

1 Zoonoses: It is important to be aware that animals in the shelter may have a disease that is transmissible to humans (zoonosis) and, even more likely, a disease transmissible to other animals. The situation postmortem is no different than when the animal was alive, however, exposure to some agents is higher when a necropsy is performed (e.g. blood‐borne pathogens, anthrax, rabies, and some fecal pathogens). The necropsy should be performed in a quiet, isolated, well‐ventilated space. Precautions should be taken consistently (protective clothing, gloves, mask) during a necropsy, and any unfixed tissues should be placed in leak‐proof containers or disposed of as medical waste according to the protocols specified by the state or institution.

2 Handling cadavers: If the necropsy cannot be carried out immediately, cadavers should be stored in a refrigerator (+2 °C to +4 °C) as soon as possible after death until the necropsy can be performed. A cadaver should be frozen only if necessary; while still present in the tissue, some microbes will not be viable after freezing.

3 Euthanasia: Euthanasia policy and strategy is widely variable among shelters. The method of euthanasia should always be documented. There are both gross and histologic sequelae to any form of euthanasia, and it is important to understand whether a lesion is “real” or simply related to the method of euthanasia. For example, intra‐abdominal administration of pentobarbital can result in puncture trauma, a layer of chemically induced necrosis on the surfaces of abdominal organs, or in peri‐mortem intra‐abdominal hemorrhage (See Figure 5.2).

Also, because euthanasia solution is caustic, intra‐abdominal administration of euthanasia solution is not the best route of administration if an animal has an enteric (gastrointestinal) disease and histopathological analysis is anticipated.

The clinical history (including duration) and knowledge about any therapy are both vital to the appropriate interpretation of findings. In a shelter with the capacity to provide medical resources, necropsy may be limited to animals that have received medical care, such as antibiotics, which can compromise postmortem culture results. It is always beneficial to perform a necropsy on a more recently affected or moribund animal, rather than one that had recovered but might be weakened and subject to a secondary disease process.

Figure 5.2 Euthanasia can cause artifactual changes to tissues. Here the granular, dull texture of the region of lung defined by the arrows is caused by intrathoracic contact with beuthanol during intracardiac euthanasia.