Histological Properties
There was no significant difference in the proportions
of fiber types in breast muscle among genotypes, with
the white fibers accounting for 93 to 96% of the total
(Table 3). The dominance of this fiber type is also obvious
from Figure 1. Von Lengerken et al. (2002) even found
99.5 and 99.8% of white fibers in the pectoralis muscle
of broilers and turkeys, respectively. In the thigh muscle,
the indigenous strains, especially when compared with
Rhode chickens, had more (P < 0.05) red and intermediate
fibers at the cost of white fibers (with the latter being
much lower in percentage compared with the breast
muscle in all groups; Figure 1). In the imported breeds,
this probably reflects breeding for higher muscle accretion,
which is often associated with a shift from oxidative
to glycolytic muscle metabolism (Jurie et al., 1995) and,
at very high selection intensity (which is probably not
yet the case for Bresse and Rhode), a higher frequency
of meat-quality problems. The cross-sectional areas of
the breast muscle fibers, independent of their type, were
smallest in Thai chickens, intermediate in Black-boned
chickens, and highest in the imported breeds (P < 0.05).