Influence of Woody Breast Myopathy on Sarcomere Length and Tensile Strength in Commercial Broiler Pectoralis major Muscle

T Eero J Puolanne,Per Ertbjerg,Cristina G Costandache

doi:10.22175/mmb.11564

Abstract

Woody breast syndrome is characterized by degenerative changes at the muscle fiber level and accumulation of connective tissue between the fibers. This study explored effects of the syndrome on muscle properties by focusing on a comparison of the sarcomere lengths between normal and woody breast muscles, including cranial and middle parts, surface and deeper layers, electrically stimulated and nonstimulated muscles, and their combinations. Tensile strengths longitudinally and transversally to the muscle fiber direction in the cranial and middle parts of the muscles were determined. The overall sarcomere lengths of woody breasts were longer than normal muscles (1.93 μ m vs. 1.88 μm; P &lt; 0.05). The surface layer had overall longer sarcomere lengths than the deeper layer (cranial surface vs. cranial deeper layer: 1.97 vs. 1.89 μ m; middle surface vs. middle deeper layer: 1.93 vs.1.84 μ m; P &lt; 0.05). Compared with normal breast muscles, woody breast muscles had longer sarcomeres in the surface layer; however, sarcomere length did not differ in the deeper layer. Electrically stimulated chicken breasts generally had longer sarcomere lengths (2.00 vs. 1.82 μm; P &lt; 0.001). There was no significant difference in tensile strength between normal and focal woody breast (mild local lesion, usually in the cranial end) samples when fiber direction or sample location was studied (P &gt; 0.05), but there was a clear difference between normal and focal versus diffuse (severe woody breast lesion throughout the muscle) samples (P &lt; 0.001). Tensile strength was much greater in diffuse woody breast muscles when extended longitudinally or transversely to the fiber direction. In conclusion, although this study did not show sarcomere lengths in living muscle, it suggests an imbalance in sarcomere lengths in different parts of the breast muscle, which may induce a reduction in the functionality and strength of the muscle.

Highlights

Woody breast syndrome (Sihvo et al, 2014) is a relatively new degenerative disease in broiler breast muscle that affects the Pectoralis major muscle and often coexists with another emerging breast muscle syndrome, white striping (Kuttappan et al, 2013)
Analysis of main effects showed slightly longer (P < 0.05) sarcomere lengths in woody breast compared with normal samples, in surface compared with deep samples, and in electrical stimulated compared with nonstimulated samples
The interactions of woody breast and electrical stimulation and electrical stimulation and location showed that the longer sarcomere lengths from electrical stimulation negated the woody breast and location effects on sarcomere length

Summary

Introduction

Woody breast syndrome (Sihvo et al, 2014) is a relatively new degenerative disease in broiler breast muscle that affects the Pectoralis major muscle and often coexists with another emerging breast muscle syndrome, white striping (Kuttappan et al, 2013). The great significance of these syndromes, which cause marked quality and possibly animal welfare problems (Norring et al, 2019), has resulted in many published papers during the last 6 to 8 y. All of the 3 syndromes may coexist, which suggests that they may have the same triggering causes (Petracci et al, 2019), but further research on mechanisms is still needed. Possible risks in animal welfare have motivated more fundamental research to identify the mechanisms of the syndromes to alleviate the problems (Norring et al, 2019). Woody breast syndrome causes degenerative changes at the muscle fiber level as well as accumulation of connective

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