Interactive Effects of Dietary Guanidinoacetic Acid and Energy Density on Growth Performance, Carcass Characteristics, Meat Quality, and Heat Stress Tolerance in Broilers

Guanidinoacetic acid (GAA), a natural precursor of creatine, plays a pivotal role in cellular energy metabolism. This study investigated the effects of dietary GAA supplementation at varying levels (0, 0.6, and 1.2 g/kg) combined with standard or reduced (−100 kcal/kg) dietary energy on growth performance, carcass characteristics, meat quality, and heat stress tolerance (during the finisher phase) in broiler chickens. A total of 360 one-day-old male Ross-308 broiler chicks were randomly allocated to 36 floor pens in a 3 × 2 factorial arrangement under a completely randomized design. Six treatments with six replicates, each having 10 birds, were evaluated over 35 days. Growth performance parameters were recorded weekly. On day 35, samples were collected for carcass characteristics (dressing percentage, breast and thigh yield, and organ weights), meat quality analysis (drip loss, cooking loss, and color parameters), and heat stress response. The heat stress response (panting frequency) was recorded during the finisher phase of the trial. GAA supplementation at 1.2 g/kg significantly (p < 0.001) improved final body weight, total weight gain, feed conversion ratio, dressing percentage, breast yield, and thigh yield. Meat quality parameters showed significant improvement (p < 0.001) with GAA in a dose-dependent manner for drip loss, cooking loss, and all color parameters (L*; a*; b*). Significant GAA × energy interactions (p < 0.001) were observed for final body weight, total weight gain, feed intake, FCR, cooking loss, live body weight at slaughter, breast yield, liver weight, gizzard weight, intestine weight, and panting frequency. The effect of GAA on heat stress tolerance was context-dependent, with a significant GAA × energy interaction (p < 0.001) for panting frequency. Under reduced-energy conditions, 1.2 g/kg GAA decreased panting frequency, suggesting improved thermoregulatory capacity, while under standard-energy conditions, GAA increased panting frequency. The main effect of GAA on panting frequency was not significant (p = 0.38), while the main effect of energy was highly significant (p < 0.001). In conclusion, GAA supplementation at 1.2 g/kg significantly improves growth performance, feed efficiency, meat quality (reduced drip and cooking losses and improved color parameters), and carcass yield in broiler chickens. Importantly, GAA supplementation largely compensated for a 100 kcal/kg reduction in dietary energy while maintaining performance. These findings support GAA as a promising nutritional strategy for sustainable broiler production, particularly in hot-climate regions.