ABSTRACT
Muscle satellite cells (MSCs) are myogenic stem cells that play a critical role in post-hatch 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-days-old 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+ (P = 0.046), and Myf-5+:MyoD+:Pax7+ (P = 0.048) MSC were greater in WB score 1 birds compared with WB score 0 and 2 birds. Overall, alterations in the resident MSC and macrophage populations and collagen protein content were observed in WB-affected muscle. Further investigation will be required to determine how these changes in cell population kinetics and local autocrine and paracrine signaling are involved in the apparent dysregulation of muscle maintenance in WB-affected broilers.
ABSTRACT
Phytogenics have been reported to improve growth performances in farm animals and are thereby considered as potential key solutions for antibiotic-free livestock nutrition. Yet, their effects on meat quality are still not well defined; therefore, the aim of this study was to determine the effects of 5 experimental phytogenic additives (3 dietary and 2 water supplements) on growth and meat quality in broilers. One-day-old broiler chicks (n = 576) were assigned to 48 floor pens and divided into 6 treatments (Control, AV/HGP/16 premix [AVHGP], Superliv concentrate premix [SCP], bacteriostatic herbal growth promotor [BHGP], AV/SSL/12 [AVSSL], and Superliv Gold [SG]) in a complete randomized design (8 pens/treatment with 12 birds/pen, and 96 birds/group). Feed intake and BW were recorded, and birds were processed at 42 d to evaluate carcass traits. Breast muscle tissues were excised to determine stress- and antioxidant-related genes expression. Both AVSSL- and SG-treated broilers produced heavier (P < 0.05) slaughter weights compared with the control-fed broilers, whereas AVSSL supplementation decreased (P < 0.05) fat pad size and increased (P < 0.05) breast weights compared with the control-fed broilers. Although pH and a* values remained unchanged, L* was decreased (P < 0.05) in all treatment and b* was reduced (P < 0.05) in SG when compared with controls. The trained sensory panelists detected more (P < 0.05) green herb flavor in the breast meat from AVHGP than SCP, SG, and control birds. The expression of superoxide dismutase 2, extracellular signal-regulated kinase 1/2, and JNK gene was upregulated in AVHGP and BHGP compared with the control (P < 0.05). Together, these results indicated that phytogenic additives might improve meat quality of broilers through modulation of stress- and antioxidant-related pathways.