Effects of dietary essential oils-organic acids preparation alone and in combination with NSP enzymes on growth...

The interactive effects of microencapsulated essential oils-organic acids preparation (EOA) and non-starch polysaccharide (NSP) enzymes on intestinal health of broilers fed wheat-based diets remain poorly elucidated. This study aimed to investigate the effects of dietary supplementation with EOA alone and in combination with NSP enzymes on growth performance, slaughter characteristics, serum biochemical indexes, and intestinal microenvironment of broilers fed wheat-based diets. A total of 360 1-d-old male Arbor Acres broilers were randomly allocated to five treatment groups for 42 d (n = 6 replicates/treatment, 12 birds/replicate): the basal diet supplemented with 200 mg/kg EOA (A), 400 mg/kg EOA (B), 200 mg/kg NSP enzymes (C), along with 200 mg/kg NSP enzymes plus 200 mg/kg EOA (D), and 200 mg/kg NSP enzymes plus 400 mg/kg EOA (E), respectively. Growth performance was monitored on days 1, 21, and 42; slaughter characteristics, serum biochemical indexes, and jejunal digestive enzyme activities were assessed on day 42; and jejunal villus morphology on days 21 and 42 was measured using hematoxylin and eosin (HE) staining. Additionally, on day 42, jejunal gene expression was analyzed by qPCR, cecal short-chain fatty acids (SCFAs) content was determined using gas chromatography (GC), and cecal microbiota composition was characterized via 16S rRNA gene sequencing. Data were analyzed using one-way analysis of variance (ANOVA) followed by Duncan's multiple range test, and statistical significance was set at P < 0.05. Results showed that compared with the single enzyme-added group (group C), dietary addition of EOA alone and combined with NSP enzymes had no significant impacts on the growth performance, slaughter characteristics, and serum biochemical indexes of broilers (P > 0.05). However, group D exhibited a 23% decrease in jejunal crypt depth and a 37% increase in villus height to crypt depth ratio (VH/CD) on day 21, and a 29% decrease in crypt depth with a 36% increase in VH/CD on day 42 compared with group C (P < 0.05). Single EOA supplementation significantly decreased jejunal trypsin activity, with 53% and 50% reductions in group A and group B, respectively, relative to group C (P = 0.035). For cecal SCFAs, group B showed a 69% decrease in isovaleric acid content (P = 0.012), while group D had a 73% increase in butyric acid content and a 34% increase in total SCFAs content compared with group C (P < 0.05). In group E, the jejunal mRNA expression of IFN-γ was upregulated 2.0-fold, and the relative abundance of Bacteroides_fragilis in the cecum was reduced by 42% when compared with group C (P = 0.001 and P = 0.034, respectively). Collectively, these findings indicate that the combined application of NSP enzymes with low-dose EOA (200 mg/kg) in wheat-based diets can optimize the intestinal microenvironment of broilers by reducing crypt depth, elevating the VH/CD ratio, and increasing the content of cecal butyric acid and total SCFAs, without compromising growth performance. In contrast, the combination of NSP enzymes with high-dose EOA (400 mg/kg) triggers intestinal microbial dysbiosis and intestinal inflammatory responses in broilers. Therefore, high-dose EOA is not recommended for combined supplementation with NSP enzymes in wheat-based broiler diets under conventional conditions.