Growth and nutrient utilization responses to xylanase and protease in broilers fed diets with reduced energy and amino acid levels

This study investigated the effects of dietary supplementation with protease and xylanase, individually or in combination, on broilers fed diets with reduced energy and essential amino acids (lysine, methionine + cysteine, and threonine) levels. A total of 280 male Ross 308 broilers were randomly assigned to five treatments: a positive control (PC) with adequate nutrients; a negative control (NC) with 100 kcal/kg reduced energy and 4% lower amino acids; NC supplemented with protease (NCP); NC with xylanase (NCX); and NC with both protease and xylanase (NCPX). Statistical analyses were conducted using the general linear model (GLM) procedure for one-way analysis of variance (ANOVA), with significance declared at p < 0.05. Broilers in the NCP group showed higher (p < 0.01) body weight and average daily gain (ADG) compared to the NC group during overall (days 11-35) period. Feed conversion ratio (FCR) was improved in all enzyme-supplemented groups relative to NC (p < 0.001), with no differences in feed intake (p > 0.05) during all phases. Apparent ileal and jejunal digestibility of crude protein and crude fat were increased in the NCP, NCX, and NCPX groups compared to NC (p < 0.001). Additionally, NCPX supplementation resulted in improved villus height and villus height-to-crypt depth ratio at day 21 (p < 0.05), indicating enhanced intestinal structure and absorptive potential. Carcass traits, including dressing percentage, breast and leg yields, and abdominal fat, did not differ significantly among treatments (p > 0.05). In conclusion, the combined supplementation of protease and xylanase effectively mitigated the adverse effects of nutrient reduction by enhancing growth performance, nutrient digestibility, and gut morphology. These findings suggest that xylanase and protease supplementation, either individually or in combination, can help improve feed efficiency and nutrient utilization in broilers fed diets with reduced energy and amino acid levels.