Heat stress mediates changes in fecal microbiome and functional pathways of laying hens

The Effects of Temperature on Animal Gut Microbiomes

Temperature is a prominent abiotic environmental variable that drives the adaptive trajectories of animal lineages and structures the composition of animal communities. Global temperature regimes are expected to undergo rapid shifts in the next century, yet for many animal taxa we lack an understanding of the consequences of these predicted shifts for animal populations. In this review, we synthesize recent evidence that temperature variation shapes the composition and function of animal gut microbiomes, key regulators of host physiology, with potential consequences for host population responses to climate change. Several recent studies spanning a range of animal taxa, including Chordata, Arthropoda, and Mollusca, have reported repeatable associations between temperature and the community composition and function of the gut microbiome. In several cases, the same microbiome responses to temperature have been observed across distantly related animal taxa, suggesting the existence of conserved mechanisms underlying temperature-induced microbiome plasticity. Extreme temperatures can disrupt the stability of alpha-diversity within the gut microbiomes individual hosts and generate beta-diversity among microbiomes within host populations. Microbiome states resulting from extreme temperatures have been associated, and in some cases causally linked, with both beneficial and deleterious effects on host phenotypes. We propose routes by which temperature-induced changes in the gut microbiome may impact host fitness, including effects on colonization resistance in the gut, on host energy and nutrient assimilation, and on host life history traits. Cumulatively, available data indicate that disruption of the gut microbiome may be a mechanism by which changing temperatures will impact animal fitness in wild-living populations.

16S rRNA gene sequencing reveals an altered composition of the gut microbiota in chickens infected with a nephropathogenic infectious bronchitis virus

Infectious bronchitis virus (IBV), a member of the Coronaviridae family, causes serious losses to the poultry industry. Intestinal microbiota play an important role in chicken health and contribute to the defence against colonization by invading pathogens. The aim of this study was to investigate the link between the intestinal microbiome and nephropathogenic IBV (NIBV) infection. Initially, chickens were randomly distributed into 2 groups: the normal group (INC) and the infected group (IIBV). The ilea were collected for morphological assessment, and the ileal contents were collected for 16S rRNA gene sequencing analysis. The results of the IIBV group analyses showed a significant decrease in the ratio of villus height to crypt depth (P < 0.05), while the goblet cells increased compared to those in the INC group. Furthermore, the microbial diversity in the ilea decreased and overrepresentation of Enterobacteriaceae and underrepresentation of Chloroplast and Clostridia was found in the NIBV-infected chickens. In conclusion, these results showed that the significant separation of the two groups and the characterization of the gut microbiome profiles of the chickens with NIBV infection may provide valuable information and promising biomarkers for the diagnosis of this disease.

Changes in the cecal microbiota of laying hens during heat stress is mainly associated with reduced feed intake

The aim of the present study was to examine the effect of high temperature on the cecal microbiota of laying hens and analyze the correlation between variation in feed intake, body temperature, and the relative abundance of specific bacterial genera. Two hundred and sixteen 28-wk-old Hy-Line laying hens were randomly divided into 3 groups with 6 replicates and raised in 3 controlled climate chambers. Birds were allocated to either a thermoneutral group (TC, 21 ± 1°C, ad libitum), high cyclic temperature group (HT, 29-35°C, ad libitum), or a pair-feeding group (PF, 21 ± 1°C, pair-feeding on the daily feed intake of HT hens) for 4 wk. There was no significant difference in diversity estimators of laying hens between the HT and TC or PF groups (P > 0.05). Principal component analysis (PCoA) based on unweighted UniFrac distance showed that the HT group did not form a distinct cluster that was clearly separated from the PF group, but was separated from the TC group. Similarity analysis (ANOSIM) confirmed that the TC group was significantly different from the HT (R = 0.259, P = 0.020) and the PF (R = 0.348, P = 0.011) groups, but the HT group was similar with the PF group (R = 0.107, P = 0.153). In addition, there was a significant correlation between feed intake and principal coordinate 1 (PC1) in PCoA (R = -0.494, P = 0.037), but no correlation between core temperature and PC1 (R = 0.025, P = 0.923). Linear discriminant analysis identified 15 genera that discriminated between the HT and TC groups (score ≥2). Among these, the feed intake was significantly related with the relative abundance of 10 genera, however, the core temperature was only significantly correlated with one specific genus. In conclusion, a high cyclic temperature of 29-35°C had significant effects on microbial composition and structure of laying hens, which was mainly related with decreased feed intake.

Effects of dietary supplementation with l-arginine on the intestinal barrier function in finishing pigs with heat stress

Previous studies showed heat stress reduces body weight gain and feed intake associated with damaged intestinal barrier function, and l-arginine (L-Arg) enhanced intestinal barrier function in young animals under stress. The aim of this study was to evaluate effects of L-Arg on serum hormones, intestinal morphology, nutrients absorption and epithelial barrier functions in finishing pigs with heat stress. Forty-eight finishing pigs (Landrace) were balanced for sex and then randomly assigned to six groups: TN group, thermal neutral (22°C, ~80% humidity) with a basal diet; HS group, heat stress (cyclical 35°C for 12 hr and 22°C for 12 hr, ~80% humidity) with a basal diet; PF group, thermal neutral (22°C, ~80% humidity) and pair-fed with the HS; the TNA, HSA and PFA groups were the basal diet of TN group, HS group and PF group supplemented with 1% L-Arg. Results showed that HS decreased (p < .05) the thyroxine concentrations and increased (p < .05) the insulin concentrations in serum compared with the TN group, but 1% L-Arg had no significant effects on them. Both HS and PF significantly increased (p < .05) the mRNA expression of cationic amino acid transporters (CAT1 and CAT2) and decreased the mRNA expression of solute carrier family 5 member 10 (SGLT1) in the jejunum compared with the TN group. Compared with the TN group, HS reduced the expression of tight junction (TJ) protein zonula occluden-1 (ZO-1) and occludin, but PF only decreased ZO-1 expression in the jejunum. Results exhibited that dietary supplementation with 1% L-Arg improved the intestinal villous height, the ratio of villous height to crypt depth, and the expression of occludin and porcine beta-defensin 2 (pBD2) in the jejunum of intermittent heat-treated finishing pigs. In conclusion, dietary supplementation with 1% L-Arg could partly attenuate the intermittent heat-induced damages of intestinal morphology and epithelial barrier functions in finishing pigs.

Effects of acute heat stress on intestinal microbiota in grow-finishing pigs, and associations with feed intake and serum profile

AIMS

This study was conducted to assess the effects of acute heat stress (HS) on intestinal microbiota, and the associations with the changes in feed intake (FI) and serum profile.

METHODS AND RESULTS

Twenty four individually housed pigs (Duroc × Large White × Landrace, 30 ± 1 kg body weight) were randomly assigned to receive one of three treatments (8 pigs/treatment): (i) thermal neutral (TN) conditions (25 ± 1°C), (ii) HS conditions (35 ± 1°C), (iii) pair-feeding (PF) with HS under TN conditions. After 24-h treatment, pigs were monitored to assess FI, and samples of serum and faeces were collected to investigate serum profile, microbial composition and short chain fatty acids (SCFAs). The results showed that HS decreased (P < 0·05) FI compared with the TN group. Compared with TN group, HS changed the serum profile by affecting biochemical parameters and hormones related with energy metabolism and stress response; immune indicators were also altered in HS group. Most of changes in serum profile were independent of FI reduction. Additionally, HS shifted the diversity and composition of faecal microbial community by increasing (P < 0·05) Proteobacteria and decreasing (P < 0·05) Bacteroidetes. Moreover, HS decreased (P < 0·05) the concentrations of propionate, butyrate, valerate, iso-valerate and total SCFAs in faeces in an FI-independent manner. Furthermore, the Spearman correlation analysis implied that changes of serum profile have potential correlation with alterations of faecal microbiota and their SCFAs metabolites in acute HS-treated grow-finishing pigs.

CONCLUSIONS

Metabolism disorders caused by 24-h acute HS associated with changes of faecal microbiota and their SCFAs metabolites in an FI-independent manner in grow-finishing pigs.

SIGNIFICANCE AND IMPACT OF THE STUDY

These results give us a new insight of the intestinal damage caused by acute HS and the underlying mechanisms.

Heat stress affects fecal microbial and metabolic alterations of primiparous sows during late gestation

Background

Heat stress (HS) jeopardizes intestinal barrier functions and augments intestinal permeability in pigs. However, whether HS-induced maternal microbial and metabolic changes in primiparous sows during late gestation remains elusive. We present here, a study investigating the fecal microbial and metabolic responses in late gestational primiparous sows when exposed to HS.

Methods

Twelve first-parity Landrace × Large White F1 sows were randomly assigned into two environmental treatments including the thermoneutral (TN) (18–22 °C; n = 6) and HS (28–32 °C; n = 6) conditions. Both treatments were applied from 85 d of gestation to farrowing. The serum and feces samples were collected on d 107 of gestation, for analyses including intestinal integrity biomarkers, high-throughput sequencing metagenomics, short-chain fatty acid (SCFA) profiles and nontargeted metabolomics.

Results

Our results show that HS group has higher serum Heat shock protein 70 (HSP70), lipopolysaccharide (LPS) and lipopolysaccharide-binding protein (LBP) levels. The gut microbial community can be altered upon HS by using β-diversity and taxon-based analysis. In particular, the relative abundance of genera and operational taxonomic units (OTUs) related to Clostridiales and Halomonas are higher in HS group, the relative abundance of genera and OTUs related to Bacteroidales and Streptococcus, however, are lower in HS group. Results of metabolic analysis reveal that HS lowers the concentrations of propionate, butyrate, total SCFA, succinate, fumarate, malate, lactate, aspartate, ethanolamine, β-alanine and niacin, whereas that of fructose and azelaic acid are higher in HS group. These metabolites mainly affect propanoate metabolism, alanine, aspartate and glutamate metabolism, phenylalanine metabolism, β-alanine metabolism, pantothenate and CoA biosynthesis, tricarboxylic acid cycle (TCA) and nicotinate and nicotinamide metabolism. Additionally, correlation analysis between significant microbes and metabolites indicated that the HS-induced microbiota shift is likely the cause of changes of intestinal metabolism.

Conclusions

Taken together, we reveal characteristic structural and metabolic changes in maternal gut microbiota as a result of late gestational HS, which could potentially provide the basis for further study on offspring gut microbiota and immune programming.

Integrating miRNA and mRNA expression profiles in plasma of laying hens associated with heat stress

High temperature is one of the most common environmental stressors plaguing animal husbandry worldwide. Little is known about the regulatory roles of miRNAs in response to heat stress in laying hens. To systematically identify heat stress-responsive miRNAs and their targets in laying hens, the differential expression of miRNAs and mRNAs was compared under heat stress and normal temperature. We identified 16 miRNAs and 502 genes that were significantly changed in heat-stressed laying hens. By comparing the differentially expressed genes (DEGs) and the putative targets of the altered miRNAs based on bioinformatics prediction, 82 coordinated genes were identified. Gene ontology classification analyses of the 82 putative target genes showed that the biological category 'cellular response to stress' was prominently annotated. Notably, the response-related gene autophagy-related protein 9A was most likely controlled by the upregulated miRNAs gga-miR-92-5p, gga-miR-1618-5p, gga-miR-1737, and gga-miR-6557 in response to heat stress. Analysis of DEGs also revealed an increase in lipid metabolism in heat-stressed laying hens. Some of these genes were negatively correlated with the altered miRNAs, suggesting that they are potential targets of the miRNAs. Taken together, our results advance our understanding of the regulatory mechanism of heat-stress-induced injury in laying hens, specifically with regard to miRNAs.