Evaluation of broiler chicken strain and diet on growth performance, carcass yield, Wooden Breast incidence, severity, and Pectoralis major compression properties

Abstract

Broiler production has advanced significantly, increasing global output by 68% from 1992 to 2022 through improved genetics, nutrition, and management practices. However, rapid growth and higher breast yields have also resulted in broilers with the Wooden Breast (WB) meat quality defect. WB results in muscle rigidity, fibrosis, and quality defects, costing the U.S. industry $200 million annually, with its etiology still unclear. Previous research demonstrated that reducing metabolizable energy (ME), digestible lysine (dLys), and digestible methionine (dMet) delays but does not prevent WB in fast-growing (FG) broilers. While lowering growth rates and breast yield may mitigate WB severity, trade-offs include reduced meat yield, higher costs, and lower productivity, limiting commercial use but still offering a valuable tool for research applications. Manual palpation is the standard method for assessing WB severity in commercial and research settings due to its practicality, but it is subjective, especially for mild cases, necessitating objective validation through mechanical methods such as compression analysis. This study aimed to evaluate the feasibility of using a slow-growing (SG) broiler strain as an unaffected control in WB research and to validate manual palpation, the primary diagnostic method for WB, through objective mechanical compression analysis (CA). Fast-growing broilers were fed either a control commercial diet (FGC) or a reduced-energy, reduced-amino acid diet (FGR), while SG broilers were fed the control diet (SGC). Birds were reared in floor pens, and body weight (BW), feed intake (FI), and WB severity were assessed weekly. On d 47 post-hatch, birds were processed, and Pectoralis major muscle compression (PMC) properties of breast fillet were assessed. Data were analyzed as a 1-way ANOVA using SAS (v9.4) PROC GLIMMIX and PDIFF for mean separation at P ≤ 0.05. Spearman correlation analysis was used to determine the association between WB score and PMC. Slow-growing broilers had higher initial BW than FG (P < 0.0001); FGC were heaviest and SGC were lightest on d 46 (P < 0.0001). Fast-growing broilers fed the R diet yielded the heaviest carcasses and breast yield, and SGC yielded the lightest (P < 0.0001). Fast-growing broilers fed the R diet consumed the most feed overall and SGC the least (P < 0.0001). Feed conversion ratio was the lowest in FGC and greatest in SGC (P < 0.0001). Notably, SGC broilers maintained 100% normal fillets throughout the study, whereas FGC broilers were 100% WB-affected by d 28 (P < 0.0001). Fast-growing broilers fed the C diet and FGR breast fillets with WB score 3 were tougher and firmer compared to SGC fillets and those with WB score 0 (P < 0.0001). Cranial portions of the fillets among all treatments were toughest and firmest, the medial portion intermediate and caudal the least firm and tough. Furthermore, live WB scores were positively and strongly correlated with PMC values (r² = 0.77; P < 0.0001), validating the reliability of the manual palpation method for WB assessment. These findings demonstrate the utility of SG broilers as a control model in WB research and confirm the reliability of the 4-point palpation system for assessing WB severity. Future efforts should focus on optimizing current WB diagnostic approaches to enhance their predictive power and applicability in both research and industrial settings, for both live birds and carcasses. Additionally, muscle immunofluorescence cryohistology analysis should be employed to validate performance data and postmortem sampling results.