Characterization of Pectoralis Major Muscle Satellite Cell Population Heterogeneity, Macrophage Density, and Collagen Infiltration in Broiler Chickens Affected by Wooden Breast

Abstract

Muscle satellite cells (MSCs) are myogenic stem cells that play a critical role in posthatch skeletal muscle growth and regeneration. Activation of regeneration pathways to repair muscle fiber damage requires both the proliferation and differentiation of different MSC populations as well as the function of resident phagocytic cells such as anti-inflammatory and pro-inflammatory macrophages. The Wooden Breast (WB) phenotype in broiler chickens is characterized by myofiber degeneration and extensive fibrosis. Previous work indicates that the resident MSC populations expressing the myogenic regulatory factors, Myf-5 and Pax7 are larger and more proliferative in broilers severely affected with WB vs. unaffected broilers. To further characterize the cellular and molecular changes occurring in WB-affected muscles, samples from pectoralis major (PM) muscles with varying severity of WB (WB score 0 = normal; 1 = mildly affected; 2 = severely affected) were collected at 25 and 43 days post-hatch (n = 8 per score per age) and processed for cryohistological and protein expression analyses. Collagen per field and densities of macrophages and MyoD+, Myf-5+, and Pax7+ MSC populations were quantified on immunofluorescence-stained cryosections. Relative collagen protein expression was quantified by fluorescent Western Blotting. In both 25 and 43-daysold broilers, the proportion of collagen per field (P ≤ 0.021) and macrophage density (P ≤ 0.074) were greater in PM exhibiting severe WB compared with normal. At day 43, populations of MyoD+, Myf-5+:MyoD+ MSC were larger and relative collagen protein expression was greater in WB-affected vs. unaffected broilers (P ≤ 0.05). Pax7+ MSC relative to total cells was also increased as WB severity increased in 43-days-old broilers (P ≤ 0.05). Densities of Myf-5+ (P = 0.092), MyoD+ (P = 0.030), Myf5+:MyoD+

Insights Into Transcriptome Profiles Associated With Wooden Breast Myopathy in Broilers Slaughtered at the Age of 6 or 7 Weeks

“…In agreement with the on-going regenerative process in the presence of WB myopathy, numbers of total nuclei and mitotically active satellite cells were increased in the 43 day broilers compared with those of non-WB ( Meloche et al, 2018 ). However, the mitotic activity of the satellite cell population was significantly altered in WB broiler, suggesting the compromised reparative capacity of the satellite cells in the abnormal birds ( Ferreira et al, 2020 ).…”

In pursuit of a better broiler: carcass traits and muscle myopathies in conventional and slower-growing strains of broiler chickens.

“…Affected breasts can also exhibit bulging and pale areas that can be associated with the presence of exudate and hemorrhage in severely affected fillets (Barbut, 2019). Wooden breast can be classified as mild, moderate or severe and different degrees of this myopathy have been reported in many countries where fast-growing broiler chickens are raised (Kuttappan et al, 2012a;Sihvo et al, 2014;Cruz et al, 2017;Ferreira et al, 2020). Recent industry reports have suggested that about 20% of the breast fillets are affected by WB, although a wide range of incidence has been reported in different flocks and studies (as reviewed by Barbut, 2019 andPetracci et al, 2019).…”

Restricted Feeding Regimens Improve White Striping Associated Muscular Defects In Broiler Chickens

“…As revealed by the immunohistochemistry staining, PAX7 + proliferation density was signi cantly compromised by AD feeding. With this data, we could extrapolate that decreased PAX7 + density resulted in poor muscular differentiation and repair activities during the later phase of AD birds that caused hypertrophic muscle defects (41,44). From the histology standpoint, IF might contribute to normal muscle growth essential for optimal muscular cell proliferation, maintenance, and repair during broiler production.…”