Effects of carbohydrase supplementation on growth performance and estimated energy equivalence in broilers fed reduced-energy diets.

1. This study evaluated carbohydrase supplementation on growth performance, metabolisable energy (ME) equivalence and body composition of broilers fed reduced-energy diets. A total of 1440 eight-day-old male Cobb 500 broilers were distributed in a completely randomised design with eight dietary treatments, nine replicates and 20 birds per replicate. Treatments consisted of a positive control (PC) diet meeting ME requirements, a negative control (NC) diet (with a reduction of 180 kcal/kg ME) and six (NC) diets supplemented with different carbohydrase complexes containing xylanase and β-glucanase (CBH1-6 at commercial inclusion levels).2. Performance was evaluated at 21 and 35 d of age as body weight (BW), body weight gain (BWG), feed intake (FI) and feed conversion ratio (FCR). ME equivalence was estimated using regression equations from diets with graded ME levels and body composition was measured by dual-energy X-ray absorptiometry.3. Broilers fed the NC diet had lower BWG (0.84 vs. 0.90 kg; p ≤ 0.001) and BW at 21 d (1.09 vs. 1.14 kg; p ≤ 0.001) compared with the PC. Supplementation with CBH3 restored BW and BWG to values similar to PC in the starter phase and resulted in the highest estimated ME equivalence (106.9 kcal/kg in the starter phase and 36.5 kcal/kg overall), followed by CBH6 (40.2 and 12.3 kcal/kg).4. Feed intake increased only in NC+CBH3 (p ≤ 0.001), whereas FCR remained higher than PC in most treatments (p ≤ 0.005). No consistent effects were observed on lean tissue or bone mineral content, although fat was reduced in specific treatments (p ≤ 0.05).5. Carbohydrase supplementation partially alleviated the effects of ME reduction, with responses depending on enzyme complex and production phase.