Abstract: 【Objective】 This study aimed to explore and compare the effects of two different immune stress models on the growth performance and intestinal immune status of broiler. 【Method】 A total of 270 one-day-old male Ross 308 chicks were randomly divided into 3 groups,namely the control (Con) group,the coccidia and Clostridium perfringens (CP) infection group,and the lipopolysaccharide (LPS) challenge group,with 6 replicates in each group and 15 chicks in each replicate.On the 11th and 13th days of the experiment,broilers in LPS group were challenged by intraperitoneal injection of LPS.On the 12th day and from the 16th to 20th days of the experiment,broilers in CP group were respectively gavaged with coccidial vaccine and Clostridium perfringens to induce a necrotic enteritis model.The experiment was divided into two stages:the early stage (1-21 days of age) and the later stage (22-42 days of age).At the end of each stage,the body weight was measured and the growth performance was calculated.After being stunned and sacrificed,the organ indices were measured.Segments of the ileum were taken to analyze the intestinal tissue morphology and gene expression.Flow cytometry was used to determine the proportions of immune cells in the ileal lamina propria and cecal tonsils,and the sIgA content in the ileal mucosa was measured. 【Result】 ① From 22 to 42 days of age and from 1 to 42 days of age,the feed to gain ratios of broilers in CP and LPS groups were both significantly higher than those in control group (P＜0.05).② At 21 days of age,the liver index of broilers in CP group was significantly higher than that in Con group,and the spleen index was significantly higher than that in the other groups (P＜0.05).③ At 21 days of age,compared with Con group,the ileal crypt depth of broilers in CP and LPS groups were increased significantly,and the ratio of villus height to crypt depth were decreased significantly (P<0.05).Meanwhile,the ratio of villus to crypt in LPS group was significantly lower than that of CP group (P＜0.05).④ At 21 days of age,the number of CD4⁺ T cells in the ileal lamina propria of broilers in LPS group was decreased significantly,while the number of Treg cells in CP group was increased significantly (P＜0.05).The proportions of mononuclear macrophages in both models were decreased significantly (P＜0.05).In addition,the proportion of Treg cells in the cecal tonsils of LPS group was increased significantly,while the proportion of dendritic cells decreased significantly (P＜0.05).⑤ Compared with Con group,the sIgA content in the ileal mucosa of broilers in LPS group at 21 days of age was increased significantly (P＜0.05).⑥ Compared with Con group,the expression levels of MUC-2,ZO-1,Claudin-1,and Occludin genes in the ileum of broilers in LPS group at 21 days of age decreased significantly.Among them,the expression level of MUC-2 gene in LPS group was significantly lower than that in CP group (P＜0.05). 【Conclusion】 The LPS challenge suppressed intestinal innate immune cell maturation while stimulating sIgA secretion,whereas the coccidia and CP infection induced splanchnic hypertrophy and increased intestinal Treg cells.These models differentially impaired broiler growth performance and intestinal immunity through distinct mechanisms,establishing a theoretical framework for stress mitigation.

Key words: broiler chicken; immune stress model; intestinal immunity; lipopolysaccharide; Clostridium perfringens