Acute and chronic stress before slaughter change muscle chemistry in ways that alter eating quality, shelf life, and appearance. Stress activates the animal’s fight-or-flight response, mobilizing energy stores and altering blood flow; this reduces muscle glycogen available for normal postmortem metabolism and shifts the rate of pH decline after death. Temple Grandin, Colorado State University, has documented how poor handling, long transport, and crowded lairage increase physiological stress and raise the risk of quality defects. Sam R. Lonergan, Iowa State University, has described how rapid postmortem glycolysis in stressed pigs produces pale, soft, exudative meat, while prolonged pre-slaughter stress leads to dark, firm, dry meat in cattle by depleting glycogen.
Causes and biochemical pathways
Stressors such as rough handling, novel environments, mixing unfamiliar animals, heat or cold extremes, and long journeys provoke hormone release and muscle contractions that consume glycogen. When glycogen is low at death, the normal postmortem drop in pH is blunted, producing high ultimate pH associated with dark, firm, dry (DFD) meat and reduced water-holding capacity. Conversely, intense acute stress immediately before slaughter can accelerate pH decline while carcass temperature remains high, causing protein denaturation and pale, soft, exudative (PSE) meat particularly in pigs. These are established mechanisms in meat science literature and form the physiological basis for handling recommendations.
Consequences for industry and consumers
The consequences extend beyond sensory attributes. Meat quality changes influence tenderness, juiciness, color, and retail yield, and can shorten shelf life because higher pH facilitates bacterial growth. Economically, processors face downgraded carcasses, increased trimming, and consumer dissatisfaction. There are also welfare and cultural dimensions: religious and smallholder systems may use on-farm slaughter to reduce transport stress, while intensive supply chains must manage long-distance movements that amplify stress risks. Environmental factors such as extreme temperatures in different territories can make stress mitigation more difficult, requiring region-specific practices.
Mitigation strategies recommended by animal welfare and meat science experts focus on low-stress handling, shorter transport, appropriate lairage conditions, and skilled personnel to reduce fear and fatigue. Implementing these practices improves both animal welfare and the consistency of meat quality, linking ethical handling directly to economic and public-health outcomes.