Effect of protein concentrations in the diet on productive performance, carcass characteristics, and meat chemical composition of broiler chickens in the dry subtropics

Introduction: Current diets of broiler chickens tend to increase protein levels to obtain high productive variables that are achieved in combination with genetic, management, and sanitary improvements, among others. An increase in dietary crude protein levels does not always accompany an increase in broiler productive efficiency due to multiple factors involved in the production system. The objective of this study was to evaluate the effect of increasing levels of dietary crude protein (CP) on productive performance, carcass characteristics, and chemical composition of breast and thigh meat in broiler chickens raised in the dry subtropics of northeastern Mexico. Method: The study used 200, 1-day-old male Ross broiler chicks. In a completely randomized design, birds were allocated to the four treatments with five replicates (floor pens) of ten birds each. The trial was divided in two phases (starter and finisher) of 21 days each (42 days total). Treatment diets (T) for starter and finisher phases had crude protein concentrations (CP; %) of 21 and 18.1 (T1), 21.4 and 18.5 (T2), 21.8 and 18.9 (T3), and 22.2 and 19.3 (T4), respectively. Within each feeding phase, the four treatment diets were formulated to similar levels of apparent metabolizable energy. Results: Protein concentrations had no effect (P > 0.05) on weight gain, while feed intake was greater in T1 (P < 0.05) than in T2 and T3. Feed conversion was better in T2 and T4 (P < 0.05) than in T1. There was no influence of treatment on carcass weight or carcass cuts (P > 0.05). Carcass yield was greater in T1 than in T3 (P < 0.05). Breast and thigh dry matter and ether extracts were similar (P > 0.05) between treatments. Breast crude protein was greater (P < 0.05) in T2 than in T3. The lowest (P < 0.05) CP concentration in thigh meat was in T3. Discussion or Conclusion: These results indicated that in the dry subtropics area of northeastern Mexico increases in CP above the level of T2 (21.4% and 18.5% CP in starter and finisher diets, respectively) did not improve broiler chicken productive performance, carcass characteristics or meat chemical composition.