Evaluation of combined dietary strategies and management of photoperiod as means to mitigate breast muscle myopathies in broiler chickens.

Breast muscle myopathies (BMMs), including white striping (WS), wooden breast (WB), and spaghetti meat (SM), represent a major challenge in broiler production. Using a 2 × 2 factorial design, this study evaluated the main effects of dietary treatment and photoperiod modification, as well as their interaction, on BMM occurrence, productive performance, and meat quality. A total of 1 908 one-day-old male chicks were randomly assigned to four experimental groups. Birds were subjected to either a standard photoperiod (STP) or a short photoperiod (SHP), which included two additional hours of darkness compared with STP. Under both photoperiod regimens, birds received either a control diet (CON) or a dietary treatment (TRT) comprising phytase superdosing, 0.06% guanidinoacetate supplementation throughout the trial, increased amino acid density during the starter phase (+2%), and a 15% lysine reduction during the grower phases. Phytase superdosing was applied at 0.40% in the starter and grower I phases, 0.30% in grower II, and 0.20% in the finisher phase. Compared with CON, the TRT diet reduced the risk of WS and WB by 26.3 and 19.2%, respectively (P < 0.001), but increased the risk of SM by 37.7% (P < 0.001). Compared with STP, SHP reduced the risk of SM by 13.7% (P = 0.024) but increased the severity of footpad dermatitis (FPD), corresponding to a 74% greater risk (P < 0.001). Regarding meat quality, the TRT diet adversely affected ultimate pH, which was 4% lower than in CON (P = 0.003), and drip loss, which was 90% higher than in CON (P < 0.001), but increased marinade uptake by 21% (P = 0.001). SHP increased cooking loss compared with STP (23.4 vs 21.7%; P = 0.05), with no further notable effects. Compared with CON, the TRT diet increased the feed conversion ratio (1.63 vs 1.57; P < 0.001), reduced daily weight gain (80.9 vs 82.6 g/bird per d; P = 0.004), and decreased breast yield by 2.35%. Mortality was nearly halved under SHP compared with STP (2.4 vs 4.2%, respectively; P = 0.035). Overall, this study demonstrates important trade-offs between productive performance and product quality. Although interactions between diet and photoperiod were limited, their main effects, particularly those of the dietary treatment, were evident. The TRT diet effectively reduced WS and WB but increased SM occurrence and compromised productive performance and selected meat quality traits. SHP reduced mortality but increased FPD severity, with limited direct effects on BMMs. These findings highlight the need to carefully balance productivity, animal welfare, and meat quality when implementing intervention strategies in commercial poultry production.