Prevalence and associated risk factors of selected breast muscle myopathies in broiler flocks of northern Iran

This cross-sectional observational study aimed to determine the prevalence and co-occurrence of Woody Breast (WB), White Striping (WS), and Spaghetti Meat (SM) breast muscle myopathies, and to identify associated risk factors in broiler flocks across northern Iran. A total of 11,615 breast fillets were collected from 150 broiler flocks processed between April and December 2023. Fillets were macroscopically evaluated for WB, WS, and SM severity using established scoring systems. Flock demographics, rearing conditions, performance and health data were collected via structured questionnaires, and risk factors for myopathies were analyzed using logistic regression. At the fillet level, WS was the most prevalent myopathy (76.45%, 95% CI: 75.78-77.22), followed by WB (14.44%, 95% CI: 13.80-15.08) and SM (0.87%, 95% CI: 0.70-1.04). Co-occurrence of myopathies was common, particularly between WS and WB, which were simultaneously detected in 11.2% of fillets, whereas SM showed minimal overlap with the other defects. Multivariable analysis identified slaughter weight >2500 g compared to ≤ 1700 g; OR = 1.33, 95% CI: 1.01-1.74) and breast burn lesions (OR = 1.47, 95% CI: 1.02-2.11) as significant predictors of WS, while season (fall vs spring; OR = 0.50, 95% CI: 0.31-0.82) was the only variable associated with SM. Woody breast exhibited the most complex risk profile. Fast-growing strains (OR = 1.52, 95% CI: 1.20-1.92) and high transport temperatures (OR = 1.10, 95% CI: 1.03-1.17) increased WB risk, whereas heavier slaughter weight (>2500 g; OR = 0.72, 95% CI: 0.58-0.89), summer or fall processing compared to spring (OR = 0.75, 95% CI: 0.59-0.97; OR = 0.51, 95% CI: 0.51-0.74; respectively), and wood shavings bedding (OR = 0.77, 95% CI: 0.64-0.92) reduced prevalence. Associations between flock-level indicators, including feed conversion ratio (FCR) (OR = 37.59, 95% CI: 13.65-103.55), disease status (OR = 1.50, 95% CI: 1.21-1.87), and breast burn lesions (OR = 1.56, 95% CI: 1.21-2.03), and the occurrence of WB were also identified. These findings demonstrate that breast muscle myopathies are highly prevalent in Iranian broilers, with WS and WB posing major quality challenges that require integrated control strategies involving genetic selection, optimized growth, flock health, and environmental management.