The objective of this study was to optimize the non-starch polysaccharide (NSP) enzymes cocktail of the corn-miscellaneous meal-based diet for finishing pigs by using in vitro simulation method, and to analyze the effects of the optimal NSP enzymes cocktail (OEC) on dietary nutrient digestibility and intestinal microbial composition and structure of finishing pigs. Finally, it could provide data support and theoretical reference for efficient utilization of diets and precise feeding.

In experiment 1, different levels of six NSP enzymes (xylanase, β-glucanase, cellulase, α-galactosidase, β-mannanase, and pectinase) were individually and respectively added to the corn-miscellaneous meal-based diet of finishing pigs. Then, in vitro ileal dry matter digestibility (IVIDMD) was determined by gastric-small intestinal simulation digestion method in vitro. When IVIDMD reached the maximum, the supplemental level of each NSP enzyme was the coding level of NSP enzyme 0. In vitro digestion experiments were carried out according to the six-element quadratic regression orthogonal rotation combination design. Meanwhile, the optimal NSP enzymes cocktail (OEC) of the corn-miscellaneous meal-based diet was selected by establishing the six-element quadratic regression equation between IVIDMD and the supplemental level of NSP enzymes. The in vitro dry matter digestibility (IVDMD), in vitro gross energy digestibility (IVGED) and in vitro digestible energy (IVDE) of diets before and after OEC addition were determined by gastric-small intestinal-large intestinal simulation digestion method in vitro to verify the effect of OEC. In experiment 2, 16 healthy castrated barrows (117.8 ± 1.66 kg) with similar body weight were randomly divided into two groups with eight pigs in each group. The pigs in the control group were fed the corn-miscellaneous meal-based diet, and the pigs in the enzyme-addition group were fed the basal diet supplemented with OEC. On the 18th day of the experiment, the fresh feces of pigs were collected by rectal wiping method, and the diversity and relative abundance of fecal microbiome were analyzed by high-throughput sequencing analysis of 16S rRNA gene, and the function was predicted.

(1) Under the conditions of this experiment, the optimized NSP enzymes cocktail of corn-miscellaneous meal-based diet was as follows: cellulase 1 003 U·kg^-1, xylanase 18 076 U·kg^-1, β-glucanase 1 377 U·kg^-1, β-mannanase 14 765 U·kg^-1, α-galactosidase 337 U·kg^-1, and pectinase 138 U·kg^-1. (2) Adding NSP enzymes cocktail optimized by in vitro method in corn-miscellaneous meal-based diet significantly increased the IVDMD from 73.44% to 76.26% (P<0.01), the IVGED from 74.03% to 76.45% (P = 0.01), and the IVDE from 14.97 MJ·kg^-1 to 15.58 MJ·kg^-1 (P<0.01). (3) At the phylum level, a total of 12 phyla with relative abundances greater than 0.1% were selected, among which Bacteroidetes, Firmicutes, and Spirochetes were the dominant phyla, and the sum of these three phyla accounted for more than 96% in the group. (4) At the genus level, adding OEC in the diet significantly increased the relative abundance of Norank_F_F082, Norank_F_Bacteroidales_ RF16_group, Bacteroides and Roseburia (P<0.05), and Eubacterium_ruminantium_group (P = 0.083) had an increasing trend, while the relative abundance of Oscillibacter decreased significantly (P<0.05), and Clostridium_Sensu_Stricto_1 and Norank_F__Norank_O__ WCHB1-41 (P = 0.083) showed a decreasing trend (P = 0.052).

Dietary non-starch polysaccharide enzymes cocktail optimization by in vitro method increased in vitro digestibility of dry matter and energy and in vitro digestible energy of corn-miscellaneous meal-based diets in finishing pigs. It also increased the proportion of beneficial bacteria in intestinal microorganism, such as fiber decompose bacteria and butyric acid producing bacteria, and reduced the number of harmful bacteria to a certain extent, and optimized intestinal microecology.