Postmortem changes in animal carcasses and estimation of the postmortem interval

Postmortem changes in animal carcasses and estimation of the postmortem interval


After death immediately, sequence of irreversible changes occur in the body of carcass. Rate of postmortem changes is variable due to it depends on several factors.

Understanding of these postmortem changes is critical for gross or microscopic pathology at autopsy so knowing the postmortem processes and factors which affect them will help in estimation of the postmortem interval (PMI) or what is called ” Time since death “.

The PMI estimation is critically significant in human death investigations and also in veterinary forensic investigations.

Although there are many studies performed in veterinary field, very limited data are available on PMI in animals.

There are many reasons for estimating PMI in veterinary medicine; it may be useful for some issues such as duration of neglect or abuse, insurance fraud and serve to provide a more complete timeframe for alleged crime events.

Although there are many decades of research, the estimation of the time of death accuracy is not improved. No method can be used singly to accurately estimate the time of death. The time of death estimation is not accurate as it depends on circumstantial factors and environmental factors.

Methods used for PMI estimation include several changes such as gross changes, microscopic changes and ocular changes.

Post = after         mortem = death        postmortem = after death

Postmortem changes mean physical and chemical changes which occur in the body or in the carcass after death immediately and include:

  1. Algor Mortis
  2. Livor Mortis
  3. Rigor Mortis
  4. Decomposition

1- Algor Mortis

It is also known as postmortem cooling (PM Cooling)

Once death occurred, the concept of PMI estimating using algor mortis is based on the premise that body begins to cool after death and cessation of cellular activities which generate heat and maintain temperature of body in life.

After death, the body ceases to regulate its internal temperature and internal temperature begins to drop.

There are some factors that affect the rate of algor mortis as:

  • Animal species: the rate in dogs differs than the rate in pig than in horse …. Etc.
  • Body covering affect the rate of PM cooling as covered body cools slower than naked body.
  • Thin body cools faster than obese body because fat is a bad conductor for heat.
    • Young age cools quicker than older age because the surface area is large in relation to the weight.
    • Cause of death: in death due to sunstroke, asphyxia and convulsions take longer time to cool.
    • The medium in which the body is placed: in open air bodies cool faster than in closed places.

    For estimation of PMI, by this formula:

    PMI(h) = {98.6-rectal temperature(F)} / 1.52- Livor Mortis

    Also known as hypostasis or known as PM lividity.

    Livor mortis is purple red discoloration of the skin of most body parts due to blood gravity into veins, circulation cessation and loss of muscle tone.

    Compressed or pressured area in the body of the carcass will not show hypostasis because the blood vessels are occluded so, in bodies lying on their back, livor mortis will appear in the back except shoulders, buttocks and back of the legs.

    Hypostasis start to appear on skin after death by 1-2 hours in the form of light violet coloration then become gradually violet then become fixed when blood coagulated after 8-12 hours.

    Importance of livor mortis:

    • Sure sign of death.
      • Determination of time of the death.
      • Determination of body position after death because the site of livor mortis not change despite of changing the body position after 8 to 12 hours.
      • Determination of death cause:
      • Can be detected by color :

      Violet color in natural death.

      Dark violet in asphyxia.

      Bright red in carbon monoxide poisoning.

      Bluish green in H2S Toxicity

      • Can be detected by site:

      In the bodies thrown in water after death by short time, hypostasis is localized in front parts of face, chest and shoulders.

      In the bodies suspended after death by short time, hypostasis present in lower limbs, lower part of forearms, lower part of abdominal wall and external genitalia.

      • Can be detected by extent:

      Well marked in death as in asphyxia because blood will still as fluid for long time due to presence of excess of CO2 and liberation of large amount of fibrinolysine.

      3- Rigor Mortis

      It is also called postmortem rigidity (PM Rigidity).

      After death, series of biochemical reactions occur in the cardiac muscle and skeletal muscle fibers in the body especially, adenosine triphosphate (ATP) which is the source of energy for muscular contraction and relaxation.

      Absence of ATP after death is responsible for rigidity of muscles.

      After death, in the absence of oxygen, the ATP formed in the muscle from breakdown of glycogen into lactic acid and PH of muscle becomes acidic.

      After 2 to 4 hours from death there is no ATP and PM Rigidity occur.

      Rigor mortis starts to appear after death by 2 hours in small muscle of eyelids and jaw, and continues downward till the feet after 12 hours.

      Muscles start to become soft again and continue downward then rigor mortis disappear in 24 hours (in summer) and 36 hours (in winter) due to secondary flaccidity.

      Rigor mortis appearance and disappearance sequence:

      • Head and face muscles.
      • Neck muscles
      • Chest muscles
      • Upper limb muscles
      • Abdomen muscles
      • Lower limb muscles

      Factors which affect PM Rigidity:

      • Age: young age and old age have rapid onset of rigor mortis due to they have little amount of ATP.
      • Temperature: when temperature increases, the rate of ATP decomposition will increase. So high temperature lowers the duration of rigor mortis.
      • Muscular state: in athletics rigor mortis is delayed onset because there is high amount of ATP.
        • Nature of death: diseases cause great wasting and exhaustion such as TB and Cancer. So the duration becomes short.

        Importance of PM Rigidity:

        • It is a sure sign of death.
        • Determination of the time of the death because it appears 2 hours after death.
        • Help in determination of body position after death.
        • Help in determination of the cause of the death.

        Conditions related to rigor mortis:

        • Heat stiffening: occur in the bodies which exposed to heat by burning or immersion in hot liquid, rigidity of muscle occur due to coagulation of muscle protein. In this case rigor mortis not appear and still until putrefaction.
        • Cold stiffening: occur in the bodies which exposed to cold, rigidity of muscle occur due to freezing of synovial fluid. If the body is kept in warm place, the stiffening disappear and rigor mortis may be established.
        • Cadaveric spasm: occur only in some voluntary muscles immediately after death and accompanied by nervous excitation.

        It occurs in case of suicidal by gunshot, cut throat by knife, drowning and homicidal.

        There is a process called Secondary Flaccidity (general relaxation of all voluntary and involuntary muscles) occurs after rigor mortis and before decomposition.

        • Decomposition

        It is also called putrefaction and it means the postmortem changes that occur in soft tissues of the body after death.

        It has 2 components: Autolysis and Putrefaction.

        Autolysis means that the own body enzymes acting on themselves and cause tissues & cellular destruction.

        Onset in winter: 36-48 hours after death.

        Onset in summer: 18-24 hours after death.

        Signs of decomposition:

        • Greenish color present on the surface of the anterior abdominal wall.
        • Gases formation as ammonia, H2S and CO2.
        • Eye and Tongue protrusion.
        • Frothy mouth.
        • Expulsion of stomach contents from mouth
        • Expulsion of intestinal contents from anus.
        • Expulsion of uterine contents from vagina and this is called PM delivery.
        • Hair and hoof or claws are easily detached.
        • Liberation of blood from veins and coloration of the surrounding tissues with green color.

        Factors which affect decomposition rate

        • Temperature of the atmosphere as if below zero ̊c will stop the decomposition or the putrefaction. And if it is 25-40 ̊c the putrefaction will enhanced.
        • Increased humidity enhances the putrefaction.
        • The cause of the death as in case of Burns and Hemorrhage, the putrefaction will be retarded.
          • Blood content of the tissues: the putrefaction is rapid in rich blood supply as liver and gravid uterus.
          • Some chemicals may retard the putrefaction as CaCl2.

          Importance of putrefaction

          • Determination of the cause of the death.
          • Estimation of the time passed since death.

            Postmortem Interval Estimation

            Gross changes

            It is almost done immediately after death; the body starts to decompose through autolysis then putrefaction with visible changes such as rigor mortis and livor mortis.

            The body undergoes changes in color, muscle rigidity, production of odor and destruction of soft tissues.

            Microscopic changes

            Most of studies have focused on gross changes but some researches have observed changes in cellular architecture such as loss of tissue architecture.

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