Enhanced β -mannanase variants improve the performance of broilers fed reduced-energy diets with stepwise crude protein reduction

This study was carried out to evaluate whether enhanced β-mannanase could mitigate the adverse effects of lower dietary metabolisable energy and crude protein on broiler performance, nutrient utilisation, and physiological responses. A total of 300 Ross 308 broilers were assigned to five dietary treatments: a positive control (PC), a moderately reduced energy and protein negative control (NC), and NC supplemented with conventional β-mannanase (CT1), enhanced β-mannanase with glycoside hydrolase domains (CT2), or further enhanced β-mannanase with accessory peptides (CT3). Each treatment included six replicates with 10 birds per replicate. In vitro analysis showed higher (p < 0.05) in vitro digestibility by pepsin in CT2 and CT3 compared with PC and NC. In vivo, birds fed CT2 and CT3 showed higher final body weight and weight gain, along with lower feed conversion ratio, particularly during the grower and finisher phases (p < 0.05), restoring performance to levels comparable with PC. Ileal digestibility of dry matter, crude protein, and key essential amino acids (lysine, methionine, threonine, valine, and arginine) were higher in CT2 and CT3 compared with NC (p < 0.05). These improvements were accompanied by increased digesta concentrations of proteolytic enzymes (trypsin, chymotrypsin, and protease) and reduced digesta viscosity in all enzyme-supplemented treatments. Blood urea nitrogen was reduced in CT2 and CT3 (p < 0.05). Carcass evaluation revealed higher breast and thigh yields and reduced abdominal fat in CT2 and CT3 compared with NC (p < 0.05). Overall, CT2 and CT3, demonstrated higher efficacy compared with conventional CT1 in improving nutrient digestibility, growth performance, and nitrogen utilisation in broilers fed reduced-energy and protein diets.