Background:Previous studies had shown that short-term acute heat stress (HS) affected the host's metabolism and intestinal microbiota independent of feed intake (FI) reduction, and long-term calorie restriction caused intestinal morphological injuries and gut microbial alterations. However, research on the effects of constant chronic HS on intestinal microbial composition and the roles of FI reduction played in is limited. This study aimed to investigate the effects of 7-day constant chronic HS on the composition of intestinal microbes in growing-finishing pigs, and its relationship with pigs' performance, intestinal morphology, and ileal immune response. Twenty-four growing-finishing pigs (Duroc × Large White × Landrace, 30 ± 1 kg body weight) were randomly assigned to three treatments (n=8), 1) thermal neutral (TN) conditions (25 ± 1 °C) with ad libitum FI, 2) HS conditions (35 ± 1 °C) with ad libitum FI, 3) pair-fed (PF) with HS under TN conditions to discriminate the confounding effects of dissimilar FI, and the FI was the previous day's average FI of HS. The small intestinal segments (duodenum, jejunum, and ileum) and feces were collected on d 8. Results:Results indicated that HS drastically declined (P<0.05) average daily gain (ADG) and average daily feed intake (ADFI) (about 61％) in comparison with TN, and caused hyperpyrexia, meanwhile PF caused hypothermia. Morphological observation by light and electron microscopes showed that both HS and PF treatment decreased (P<0.05) the villus and microvillus height compared with TN. Additionally, HS increased (P<0.05) protein expression of heat shock protein 70 in the duodenum, jejunum, and ileum. Furthermore, the expression of tight junction protein zonula occluden-1 (ZO-1) in the duodenum and ileum, and Occludin in the ileum were enhanced (P<0.05) compared with TN and PF. Moreover, HS significantly enhanced (P<0.05) the mRNA relative expression of inflammatory cytokines (TLR-2, TLR-4, and tumor necrosis factor-α(TNF-α), IL-6, IL-8, PG1–5,β-defensin 2 (pBD-2)), mucins (mucin-1 and mucin-2) and P65 protein level in the ileal mucosa tissue. Intestinal microbiota analysis by 16S rRNA sequencing showed lower (P<0.10)αdiversity in both HS and PF, and a separated cluster ofβdiversity among groups. Compared with TN, HS but not PF mainly reduced (FDR<0.05) Bacteroidetes (phylum), Bacteroidia (class) and elevated the proportions of Proteobacteria (phylum, FDR<0.05), Bacillales (order, FDR<0.05), Planococcaceae (family, FDR<0.05), Kurthia (genus, FDR<0.05), Streptococcaceae (family, FDR<0.10) and Streptococcus (genus, FDR<0.10). Notably, Lactobacillales (order) was decreased (FDR<0.05) by PF alone. Furthermore, the Spearman correlation analysis indicated that the microbes prevalent in HS were positively (P< 0.05) associated with intestinal morphological injuries indicators and ileal immune response parameters, and the microbes reduced in HS were negatively (P<0.05) with the performance data. Conclusions:Intestinal morphological injuries and ileal immune response caused by constant chronic HS independent of FI showed close connections with alterations in intestinal microbiota in growing-finishing pigs.

Yunxia Xiong;Shuting Cao;Hao Xiao;Qiwen Wu;Hongbo Yi;Zongyong Jiang;Li Wang

State Key Laboratory of Livestock and Poultry Breeding,Key Laboratory of Animal Nutrition and Feed Science in South China Ministry of Agriculture,Maoming Branch,Guangdong Laboratory for Lingnan Modern Agriculture,Guangdong Key Laboratory of Animal Breeding and Nutrition,Institute of Animal Science,Guangdong Academy of Agricultural Sciences,Guangzhou 510640,China

畜牧与生物技术杂志（英文版）

[1]Yunxia Xiong;Shuting Cao;Hao Xiao;Qiwen Wu;Hongbo Yi;Zongyong Jiang;Li Wang-.Alterations in intestinal microbiota composition coincide with impaired intestinal morphology and dysfunctional ileal immune response in growing-finishing pigs under constant chronic heat stress)[J].畜牧与生物技术杂志（英文版）,2022(03):769-786

hyperpyrexia,microvillus,Bacillales,Planococcaceae,Kurthia

Alterations,intestinal,microbiota,composition,coincide,impaired,morphology,dysfunctional,ileal,immune,response,growing,finishing,pigs,under,constant,chronic,heat,stress,Background,Previous,studies,had,shown,that,short,term,acute,HS,affected,host,metabolism,independent,feed,intake,reduction,long,calorie,restriction,caused,morphological,injuries,gut,microbial,alterations,However,research,effects,roles,played,limited,This,study,aimed,investigate,day,microbes,its,relationship,performance,Twenty,four,Duroc,Large,White,Landrace,body,weight,were,randomly,assigned,three,treatments,thermal,neutral,conditions,libitum,fed,PF,discriminate,confounding,dissimilar,was,previous,average,small,segments,duodenum,jejunum,ileum,feces,collected,Results,indicated,drastically,declined,daily,gain,ADG,ADFI,about,comparison,meanwhile,hypothermia,Morphological,observation,by,light,electron,microscopes,showed,both,decreased,height,compared,Additionally,increased,protein,expression,shock,Furthermore,tight,junction,zonula,occluden,ZO,Occludin,enhanced,Moreover,significantly,relative,inflammatory,cytokines,TLR,tumor,necrosis,PG1,defensin,pBD,mucins,P65,level,mucosa,tissue,Intestinal,analysis,16S,rRNA,sequencing,lower,diversity,separated,cluster,among,groups,Compared,but,not,mainly,reduced,FDR,Bacteroidetes,phylum,Bacteroidia,class,elevated,proportions,Proteobacteria,order,family,genus,Streptococcaceae,Streptococcus,Notably,Lactobacillales,alone,correlation,prevalent,positively,associated,indicators,parameters,negatively,data,Conclusions,close,connections

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