Abstract: 【Objective】 The purpose of this study was to explore the proportion of compound microecological preparation in piglet feed and the effect on piglets after replacing antibiotics.【Method】 A total of 80 healthy weaned piglets (Duroc×Landrace×Yorkshire, weaned at (28±2) days, weighted (9.31±0.52) kg) were randomly divided into five groups, 4 replicates per group and 4 piglets per replicates (half male and half female), respectively.The diet in control group was basal diet.The diet in low dose group (LOW) was basal diet supplemented with 0.1% compound microecological preparation (1×10¹¹ CFU/kg).The diet in medium dose group (MED) was basal diet supplemented with 0.2% compound microecological preparation (2×10¹¹ CFU/kg).The diet in high dose group(HIG) was basal diet supplemented with 0.3% compound microecological preparation (3×10¹¹ CFU/kg).The diet in antibiotic group (ANT) was basal diet supplemented with 75 mg/kg chlortetracycline.The experiment was lasted for 28 days.The initial and final body weights, diarrhea of piglets, and feed intake of repeats were accurately recorded.Blood samples were collected on 28 days for the measurement of serum immune parameters and biochemical indices.The contents of cecum were collected, and the changes of intestinal microbiota were analyzed by 16S rRNA sequencing.【Result】 Compared with control group, ①The average daily gain (ADG) and average daily feed intake (ADFI) of MED group were significantly increased (P<0.05), and there was no significant difference between MED and ANT groups (P>0.05).The feed/gain ratio (F/G) of MED and HIG groups were decreased significantly (P<0.05), and had no significant difference compared to ANT group (P>0.05).The diarrhea rate of piglets decreased significantly in LOW and MED groups (P<0.05), and had no significant difference compared to ANT group (P>0.05).②Thymus index of MED and HIG groups, and spleen index of MED group were significantly increased (P<0.05).The thymus and spleen index of MED group were significantly higher than ANT group (P<0.05).③ The high-density lipoprotein (HDL) of the LOW, MED and HIG groups were increased significantly (P<0.05), and the serum albumin (ALB) contents of MED and ANT groups were significantly increased (P<0.05).The activity of aspartate transaminase (AST) were significantly decreased in LOW, MED and ANT groups (P<0.05).④ The serum immunoglobulin G(IgG) levels in LOW, MED and ANT groups were significantly increased (P<0.05).The immunoglobulin A(IgA) and immunoglobulin M(IgM) levels in MED and ANT groups were significantly increased (P<0.05), and there was no significant difference between MED and ANT groups (P>0.05).⑤ The relative abundance of Firmicutes were increased significantly (P<0.05), in LOW, MED and ANT groups, and the relative abundance of Prevotella_1 decreased significantly (P<0.05) in LOW and ANT groups.The relative abundance of Proteobacteria in HIG and ANT groups were significantly reduced (P<0.05).The relative abundance of Rikenellaceae and Campylobacter were decreased significantly (P<0.05), while the relative abundance of Lactobacillaceae and Lactobacillus were increased significantly (P<0.05) in LOW, MED, HIG and ANT groups.The relative abundance of Alloprevotella in HIG group was increased significantly (P<0.05).The relative abundance of Lachnospira in MED, HIG and ANT groups were decreased significantly (P<0.05).The relative abundance of Faecalibacterium in LOW, HIG and ANT groups were increased significantly (P<0.05).Compared with the control group and ANT group, the relative abundance of Pseudomonadaceae in LOW and HIG groups were decreased significantly (P<0.05), and the relative abundance of Ruminococcaceae in LOW group was increased significantly (P<0.05).【Conclusion】 Adding compound microecological preparations to the diet could improve the growth performance and immune function of weaned piglets, improve the abundance of cecal microbes, reduce the abundance of intestinal pathogenic bacteria, and reduce the rate of diarrhea.The effect of adding 0.2% compound probiotics (the number of viable bacteria was 2×10¹¹ CFU/kg) was better, and was similar to that of antibiotics.

Key words: weaned piglets; microecological preparation; growth performance; immune function; flora structure