Fiber Metabolism, Procollagen and Collagen Type III Immunoreactivity in Broiler Pectoralis Major Affected by Muscle Abnormalities

Abstract

The present study aimed to evaluate the muscle fiber metabolism and assess the presence and distribution of both procollagen and collagen type III in pectoralis major muscles affected by white striping (WS), wooden breast (WB), and spaghetti meat (SM), as well as in those with macroscopically normal appearance (NORM). For this purpose, 20 pectoralis major muscles (five per group) were selected from the same flock of fast-growing broilers (Ross 308, males, 45-days-old, 3.0 kg live weight) and were used for histochemical (nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR) and alpha-glycerophosphate dehydrogenase (α-GPD)) and immunohistochemical (procollagen and collagen type III) analyses. When compared to NORM, we found an increased proportion (p < 0.001) of fibers positively stained to NADH-TR in myopathic muscles along with a relevant decrease (p < 0.001) in the percentage of those exhibiting a positive reaction to α-GPD. In addition, an increased proportion of fibers exhibiting a positive reaction to both stainings was observed in SM, in comparison with NORM (14.3 vs. 7.2%; p < 0.001). After reacting to NADH-TR, SM exhibited the lowest (p < 0.001) cross-sectional area (CSA) of the fibers (-12% with respect to NORM). On the other hand, after reacting to α-GPD, the CSA of WS was found to be significantly larger (+10%) in comparison with NORM (7480 vs. 6776 µm²; p < 0.05). A profound modification of the connective tissue architecture involving a different presence and distribution of procollagen and collagen type III was observed. Intriguingly, an altered metabolism and differences in the presence and distribution of procollagen and collagen type III were even observed in pectoralis major muscle classified as NORM.

Keywords: NADH-TR; chicken; muscle abnormalities; procollagen and collagen type III; αGPD.

Figure 1

Serial cross-sections of pectoralis major (PM) belonging to a slow-growing genotype (A,B) are reported in comparison with the normal genotype (NORM) (A1,B1)). Few nicotinamide adenine dinucleotide tetrazolium reductase (NADH-TR)-positive fibers were detected within the pectoralis major of the slow-growing genotype ((A), arrows) whereas an intense and diffuse positivity for alpha-glycerophosphate dehydrogenase (α-GPD) activity was found ((B), arrows). In NORM, some fibers exhibiting an intense oxidative and glycolytic metabolism ((A1,B1), arrows) were found. In white striping (WS)-, wooden breast (WB)-, and spaghetti meat (SM)-affected muscles, many fibers exhibited an intense reaction to NADH-TR ((A2–A4), arrows) and α-GPD ((B2–B4), arrows). Within these muscles, we observed intensely stained, positive small-caliber regenerative fibers in correspondence with larger-caliber fibers ((A2–A4,B2–B4), arrowheads).

Figure 2

Serial cross-sections of chicken pectoralis major (PM) muscles belonging to a fast-growing genotype classified as normal cases (NORM) and those affected by white striping (WS), wooden breast (WB), or spaghetti meat (SM) abnormalities showing the immunoreaction to procollagen type III (A–A4) and collagen type III (B–B4) antibodies. Immunoreactivity to procollagen type III was almost absent in PM belonging to the slow-growing genotype, and only the fibroblasts were intensely stained ((A), arrow). Collagen type III was intensely marked and appeared normally arranged within the endomysial and perimysial compartments ((B), arrow). In NORM, immunoreactivity to procollagen was restricted to some areas of the perimysial spaces ((A1), arrow). In addition, collagen type III within the endomysial compartment was intensely labelled, whereas in the perimysial septa, intensely stained areas were intermingled to weakly marked ones ((B1), arrow). A profoundly altered muscle architecture was found in WS- and WB-affected muscle (A2,A3,B2,B3)—degenerated muscle fibers were replaced by poorly organized connective tissue immunoreactive to both procollagen and collagen type III ((A2,B2), arrowheads). The diffused connective tissue observed in (A2) and (B2) (WS muscles) was intensely stained (arrows), whereas weak immunoreactions were observed in WB-affected muscles (A3,B3) in which intensely stained collagen bundles alternated to faintly labelled ones (arrows). An evident detachment of the muscle fibers composing the PM was observed within the SM-affected muscles (A4,B4). Immunoreaction to procollagen was almost absent (only the fibroblasts were stained), while the endomysial connective tissue exhibited a strong collagen III labelling.