1. Two consecutive trials were conducted to evaluate the effects of guanidinoacetic acid (GAA) supplementation (a creatine precursor) and energy levels in broiler diets based on maize-soybean meal (Trial 1) or that additionally included poultry by-product meal (PBPM; Trial 2) on growth performance, carcass yield and breast meat quality to 41 days of age.

2. A total of 792, one-day-old male Ross 308 broiler chickens were randomly distributed into six treatments – three energy levels (sufficient AME_n or 0.2 and 0.4 MJ/kg reduced AME_n) and two GAA levels (0.00% or 0.06%) with eight replicates for each trial.

3. Reducing dietary energy resulted in poorer body weight gain (BWG) and feed conversion ratios (FCR) for each trial (P < 0.05). However, GAA supplementation improved FCR, BWG and European Production Efficiency Factor (EPEF) (P < 0.05).

4. Dietary energy level and GAA addition had no significant effect on carcass parameters, drip loss, pH and chemical composition of breast meat (P > 0.05), but decreased relative liver weight (P < 0.05).

5. It was concluded that, regardless of dietary energy levels, supplementation of GAA to plant-based diets or those including PBPM has the potential to improve growth performance in broilers.

1. 进行了两项连续试验，以评估在基于玉米豆粕（试验 1）或另外包括家禽副产品粕（PBPM）的肉鸡日粮中添加胍基乙酸（GAA）（一种肌酸前体）和能量水平的影响; 试验 2) 对 41 日龄的生长性能、胴体产量和胸肉质量。

2. 总共 792 只 1 日龄雄性 Ross 308 肉鸡被随机分配到六个处理中——三个能量水平（足够的 AME _n或 0.2 和 0.4 MJ/kg 减少的 AME _n）和两个 GAA 水平（0.00% 或0.06%），每个试验重复八次。

3. 降低日粮能量导致每次试验的体重增加（BWG）和饲料转化率（FCR）较差（P < 0.05）。然而，GAA 补充剂改善了 FCR、BWG 和欧洲生产效率因子 (EPEF) (P < 0.05)。

4.日粮能量水平和GAA添加对胴体参数、滴水量、pH值和胸肉化学成分无显着影响（P > 0.05），但降低了相对肝重（P < 0.05）。

5. 得出的结论是，无论日粮能量水平如何，在植物性日粮或包括 PBPM 的日粮中添加 GAA 都有可能提高肉鸡的生长性能。