The Effects of Pre-Slaughter Fasting Periods on Tonic Immobility, Slaughter, Carcass and Meat Quality Traits in Medium- and Fast-Growing Broiler Chickens

In this study, the effects of pre-slaughter fasting periods (8, 12, and 16 h) on stress levels, body weight loss, slaughter, carcass, and meat quality characteristics were investigated in broiler chickens with different growth rates (medium and fast-growing). In the experiment, 15 male and 15 female broilers each from the ANADOLU-T A1 (medium growing) dam line and ROSS-308 hybrid (fast growing) at 42 days of age were used. Body weight losses did not differ significantly among fasting periods, but medium-growing broilers exhibited higher body weight losses across all fasting groups (P<0.05). The carcass yield was higher in fast-growing broilers (P<0.05), while abdominal fat ratios were higher in medium-growing broilers (P<0.05). The amount of residual feed in the gizzard, digestive system, and gizzard ratios decreased with increasing fasting duration (P<0.05). Digestive system ratios also differed between genotypes (P<0.05). An increase in breast ratio was observed with longer fasting periods (P<0.05). On the other hand, the fast-growing genotype had higher breast ratios, lower wing ratios, lower back ratios, and lower neck ratios (P<0.05). Fasting periods did not significantly affect the L*, a*, and b* color values of breast and thigh meat, but differences between genotypes were significant, with higher values observed in the fast-growing genotype (P<0.05). Breast pH values did not differ among fasting periods but were higher in the fast-growing genotype (P<0.05). Thigh pH values, however, varied significantly between fasting periods and genotypes (P<0.05). The medium-growing genotype had higher thigh pH values, and thigh pH increased with longer fasting periods (P<0.05). White striping and woody breast scores in breast muscles were higher in the fast-growing genotype, with partial increases observed as fasting duration increased. In conclusion, the results indicate that a 12-h pre-slaughter fasting period is sufficient for digestive tract clearance and carcass quality. However, meat quality defects in fast-growing genotypes should be monitored.