Effects of physical exercise on meat quality characteristics of Sunit sheep.

Highlights • Long-term physical exercise before slaughter resulted in faster muscle pH decline post-mortem and more yellow meat in Sunit sheep. • Physical exercise caused a shift of muscle fibers from oxidative to glycolytic type. • Physical exercise activated skeletal muscle satellite cells influencing the process of conversion from muscle to meat. Abstract The objective of this study was to investigate the effects of muscle exercise on meat quality characteristics and protein and gene expression of Sunit sheep. To this end, 24 Sunit sheep that had the same genetic background and had been raised on extensive pasture for their first 9 months were randomly divided into two groups (12 sheep each), which were raised separately for 3 months until slaughter. The first group of sheep was kept on pasture and allowed to move freely outdoors (M Group), whereas the other group of sheep was kept in one pen on the farm (control [C] group). After slaughter, samples of the longissimus dorsi muscle were taken to evaluate meat quality. The differences in the expression of muscle-exercise-related proteins and genes between the two groups were analyzed by Western blotting and RT-PCR techniques. The results showed reductions in the pH measured 1 h and 24 h post-mortem and in the a* value (redness) for meat colour in the longissimus dorsi muscle of the sheep in the M group in comparison with those in the C group (P < 0.01), while an increasing b* value (yellowness) for meat colour was observed in the M group sheep (P < 0.01). The greater (P < 0.05) levels of Pax7 and MyoD but not PPARγ in the M group indicated that the activated skeletal muscle satellite cells underwent myogenesis rather than adipogenesis. In addition, endurance exercise caused a shift in myosin heavy chain composition from the oxidative isoform to the glycolytic form (P < 0.01), which may have resulted in the pH decline and the colour change. In conclusion, exercise-induced activation of skeletal muscle satellite cells, which regulate the pH and colour of meat, was associated with the transformation of muscle fiber types in Sunit sheep. [ABSTRACT FROM AUTHOR]