Effect of Preslaughter Handling Stress on Meat Quality in Pigs: Contribution of Skeletal Muscle Cellular Apoptosis in Response to Increased Blood Glucocorticoids

Preslaughter stress commonly exists in the meat practice of pigs. To study the effects of preslaughter stress and stress hormones on meat quality in finishing pigs, a group of 112 pigs (c.a. 100 kg) were subjected to different preslaughter handling before harvest. An in vitro stress model of skeletal muscle was also employed to identify the mechanism of stress hormones on meat quality. Most of the meat quality indices had marked changes accompanied with an exaggerated release of stress hormones (P<0.05). There were statistically significant correlations between most of the meat quality indices and stress hormones (P<0.05). In the stress model of muscle cells, DEX had significant cytotoxic effects on muscle cells associated with release of reactive oxygen species and accumulation of intranucleosomal DNA damage, and also markedly down-regulated the expression of glucocorticoids receptor α (GRα) gene. In addition, the mRNA level of Bcl-2 was down-regulated while that of BAX was up-regulated, leading to increased ratio of pro-apoptotic BAX/Bcl-2 in a dose-dependent manner. These effects could be prevented by isoconcentration of RU486. Moreover, using the bioinformatics software, potential GR response elements were found in the promoter region of porcine Bcl-2 and BAX genes. Based on these results, we hypothesize that stress hormones might exert its cytotoxic effects on muscle tissue via GRα binding to GR response element in the promoter of Bcl-2 family genes and hence up-regulate the ratio of BAX/Bcl-2 that in turn influence meat quality.