Abstract
High ambient temperatures negatively affect the human well-being as well as animal welfare and production. The gastrointestinal tract is predominantly responsive to heat stress. The currently available information about the multifaceted response to heat stress within different parts of the intestine is limited, especially in avian species. Hence, this study aims to evaluate the heat stress-induced sequence of events in the intestines of chickens. Furthermore, the gut health-promoting effect of dietary galacto-oligosaccharides (GOS) was investigated in these heat stress-exposed chickens. Chickens were fed a control diet or diet supplemented with 1% or 2.5% GOS (6 days) prior to and during a temperature challenge for 5 days (38–39°C, 8h per day). The parameters measured in different parts of the intestines included the genes (qPCR) HSF1, HSF3, HSP70, HSP90, E-cadherin, claudin-1, claudin-5, ZO-1, occludin, TLR-2, TLR-4, IL-6, IL-8, HO-1, HIF-1α) and their associated proteins HSP70, HSP90 and pan-cadherin (western blots). In addition, IL-6 and IL-8 plasma concentrations were measured by ELISA. In the jejunum, HSF3, HSP70, HSP90, E-cadherin, claudin-5, ZO-1, TLR-4, IL-6 and IL-8 mRNA expression and HSP70 protein expression were increased after heat stress exposure and a more pronounced increase in gene expression was observed in ileum after heat stress exposure, and in addition HSF1, claudin-1 and HIF-1α mRNA levels were upregulated. Furthermore, the IL-8 plasma levels were decreased in chickens exposed to heat stress. Interestingly, the heat stress-related effects in the jejunum were prevented in chickens fed a GOS diet, while dietary GOS did not alter these effects in ileum. In conclusion, our results demonstrate the differences in susceptibility to heat stress along the intestine, where the most obvious modification in gene expression is observed in ileum, while dietary GOS only prevent the heat stress-related changes in jejunum.
Highlights
Heat stress is one of the most relevant environmental stressors in poultry production worldwide [1]
The heat stressinduced damages within the intestine is a complex process and needs to be investigated in order to identify intervention strategies and this study focused on the assessment of typical alterations in the expression of a number of genes and their corresponding proteins, such as heat shock factors (HSF), heat shock protein (HSP), adherens junctions (AJ) and tight junctions (TJ), Toll-like receptor (TLR), cytokines/chemokines and oxidative stress markers, which are all related to the hypothetical cascade of events occurring in different parts of the intestine from broilers upon heat stress exposure
Heat stress resulted in a significant mRNA up-regulation of HSF3 in the chicken jejunum (Fig 1C), while in ileum both HSF1 and HSF3 mRNA levels were increased after heat exposure (Fig 1B and 1D)
Summary
Heat stress is one of the most relevant environmental stressors in poultry production worldwide [1]. The gastrointestinal tract is primarily responsive to heat stress and a variety of changes can be observed, including alterations in the microbiota and an impairment of intestinal barrier integrity [10,11]. These changes allow the translocation of luminal antigens and pathogens through the intestinal epithelium and facilitate the response of the innate immune system by exaggerating the extent of Toll-like receptor (TLR) signaling, leading to the development of intestinal inflammation and damage [12,13]. This study included experiments aiming to evaluate the possible protective role of GOS against the heat stress-induced alterations in the intestines of chickens
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