Yes, if a mammal (or fish) is agitated, afraid, startled, or otherwise psychologically disturbed, its body automatically starts to convert the carbohydrate glycogen stored in its tissues into sugar for quick energy. This natural biological reaction gives the animal greater strength to fight or take flight, thus increasing its chances for survival. However, should the animal die, any conversion that occurred will shorten the meat's storage life. After death, the glycogen remaining in the muscles converts into lactic acid, a substance that retards bacterial growth. It follows that the lower the glycogen level, the less lactic acid is produced, and therefore the shorter the amount of time the meat will stay fresh.
Every experienced deer hunter has heard the so-called chestnut that the venison will be more tender if the arrow or bullet is well targeted, slaying the animal instantly. This advice is not only humane, but also sound, because if the deer struggles, runs, and enters a state of shock before dying, it will use up much of the glycogen in its muscles. When this happens, the venison meat cannot safely be hung for very long, and therefore it will not become as tender as it should be.
For the same reasons, modern slaughterhouses kill - be it with an electric probe or whatever - with such surprise and swiftness that an animal barely has time to contemplate its fate. Some slaughterhouses go one step further and try to maintain an environment that is as serene as possible for the animal.
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