RESUMEN
Pork quality depends on various genetic and environmental factors. Despite the improvement of slaughter conditions, the PSE type is still one of the main concerns in this field. This study was conducted on nonstressed animals to evaluate the tissue characteristics of some muscles usually involved during stress compared with a reference muscle, the M. triceps brachii, which is actually not subject to stress-caused damages. Samples of M. triceps brachii, M. longissimus dorsi, M. biceps femoris, and M. semimembranosus were taken from pigs exhibiting 1 of the 3 HAL genotypes (NN, Nn, or nn) and 2 of the 3 RN genotypes (rn+rn+ or rn+RN-). Histoenzymology and immunohistochemistry were used to compare the fiber typing and capillary network in these muscles within these different stress susceptibility genotypes. In comparison with the reference muscle, M. triceps brachii, the combination of a high value of the number of type IIb fibers and a low vascular network showed a primary effect on muscles usually involved during stress. This led to the definition of a PSE index. A dramatic increase (P < 0.001) in this PSE index was systematically found in muscles usually involved in the PSE-type condition. These results show that distinctive histological characteristics were associated with the vulnerability of some muscles independently of the genotypes. Moreover, this study highlights the distinctive histological features of each genotype and is likely to suggest some interactions between them.