Research note: Influence of growing systems (conventional, organic, raised-without-antibiotics) on myopathies of broiler breast fillets

Growth‑related breast muscle myopathies, including white striping (WS), woody breast (WB), and spaghetti meat (SM), continue to challenge modern broiler production, yet limited information exists on how different production systems influence their prevalence within the same fast‑growing genotype. This study evaluated the occurrence and severity of these myopathies in broilers raised under conventional (CONV), raised‑without‑antibiotics (RWA), and organic (ORG) systems across two production years (2024 and 2025). For WS, no significant differences were observed between CONV and RWA in either year, and the ORG system (included in 2025) showed similar results. Approximately 85% of fillets exhibited noticeable WS (severity 2-3), consistent with previous reports. In contrast, WB and SM showed clearer system‑related differences. In 2024, severe WB (WB 2-3) was more prevalent in RWA birds, whereas in 2025 both ORG and RWA exhibited lower severe WB incidence than CONV. Severe WB (WB-3) remained relatively low overall. SM severity was consistently greater in RWA compared with CONV in both years, while ORG values (2025) resembled CONV. These findings suggest that RWA birds may be more susceptible to physiological stressors affecting muscle structure. Fillet weight was strongly associated with myopathy severity. WS0 fillets were the lightest, and fillets with WS, WB, or SM showed increasing severity with increasing fillet weight across all systems. In both years, CONV and ORG fillets of equivalent severity were heavier than RWA fillets. RWA birds tended to exhibit more severe myopathy at lower fillet weights, indicating system‑specific growth or stress dynamics. Overall, production system influenced the severity and distribution of WB and SM but not WS. Heavier fillets consistently exhibited more severe myopathies, underscoring the relationship between rapid growth, muscle development, and myopathy expression.