Abstract This study assessed the effects of β-mannanase (BM) supplementation on growth performance, digestive enzyme activity, cecal microbial communities, and short-chain fatty acid (SCFA) production in broiler chickens fed diets with different metabolizable energy (ME) levels. A total of 1,296 male one-d-old Cobb 500 broilers were randomly distributed in a 3 × 2 factorial arrangement (three ME levels × 0 or 200 g/ton BM), with 6 replicates per treatment combination. The three ME levels were 3,000 (ME1), 2,930 (ME2), and 2,860 (ME3) kcal/kg, respectively, during the 0–3 w-old stages and 3,150 (ME1), 3,080 (ME2), and 3,010 (ME3) kcal/kg, respectively, during the 3–6 w-old stages. Reducing ME levels increased broiler feed intake (P = 0.036) and decreased average daily gain (ADG, P = 0.002) during the entire period. While BM supplementation increased ADG (P = 0.002) and improved the feed conversion ratio (P = 0.001) during the 0–3 w-old stages, with no effect during the 3–6 w-old stages. Overall, reducing ME levels increased pancreatic lipase (P = 0.045) and amylase (P = 0.013) activity and duodenal amylase activity (P = 0.047). Notably, BM supplementation significantly increased pancreatic lipase activity (P = 0.015) and increased lipase (P = 0.029) and amylase (P = 0.025) activities in the jejunal chyme. Although diet or enzyme supplementation did not affect microbial diversity, significant differences in microbial communities were observed. At the genus level, decreasing ME levels significantly affected the average abundances of Tyzzerella (P = 0.028), Candidatus_Bacilloplasma (P = 0.001), Vibrio (P = 0.005) and Anaerotruncus (P = 0.026) among groups, whereas BM supplementation reduced the average abundances of Escherichia-Shigella (P = 0.048) and increased the average abundances of Barnesiella (P = 0.047), Ruminococcus (P = 0.020), Alistipes (P = 0.050), and Lachnospiraceae_unclassified (P = 0.009). SCFA concentrations strongly depended on bacterial community composition, and BM supplementation increased acetic acid (P = 0.004), propionic acid (P = 0.016), and total SCFA concentrations. In conclusion, BM supplementation improved the performance of younger broilers, and both enzyme supplementation and reduced ME levels positively affected digestive enzyme activity and intestinal microflora.

The effects of β-mannanase supplementation on growth performance, digestive enzyme activity, cecal microbial communities, and short-chain fatty acid production in broiler chickens fed diets with different metabolizable energy levels