Meat Science and Muscle Biology Symposium: Impact of Pre- and Post-Slaughter Handling on Meat Quality

Market weight pigs are subjected to numerous stressors during the marketing process from loading at the farm to stunning at the packing plant. These stressors have important implications for animal well-being and fresh pork quality traits. The objectives of this presentation are to review: 1) pre-harvest stressors in pigs; 2) common measures of stress during handling and transportation; and 3) effects of pre-harvest stressors on metabolic changes and fresh pork quality traits. Pre-harvest stressors can be encountered during loading, transportation, unloading, lairage, and movement to the stunning area. Although the majority of the work in this area has focused on animal handling procedures, other areas of interest include the mixing of unfamiliar pigs, transport floor space, transport time, lairage time, and environmental conditions. Genetics, previous experiences, and the physical condition of the animal will impact how pigs respond to these stressors. Measures of stress during handling and transportation include: body temperature, heart rate, respiration rate, blood acid-base balance (pH, lactate, bicarbonate, and base-excess), stress hormones (cortisol, epinephrine, and norepinephrine), enzyme activity (creatine kinase and lactate dehydrogenase), and muscle glycolytic potential. The magnitude of the change in these parameters is dependent upon stressor intensity, duration, and frequency. For example, recent work by Hambrecht et al. (2005) and Ritter et al. (2009) reported that multiple concurrent pre-harvest stressors have additive effects on body / carcass temperature, blood lactate, and muscle lactate values in market weight pigs. It is well documented that aggressive handling immediately before harvest increases early postmortem temperature and the rate of pH decline in muscle, resulting in pork with high drip loss (Hambrecht et al., 2004a; 2004b; 2005). However pre-harvest stressors that reduce muscle glycogen during loading at the farm may have beneficial effects on ultimate pH and water-holding capacity (Edwards, 2009). Therefore, improvements in pre-harvest handling do not always translate to improvements in fresh pork quality traits.