Abstract
High environmental temperature has strong adverse effects on poultry production, welfare, and sustainability and, thereby, constitutes one of the most challenging stressors. Although colossal information has been published on the effects of heat stress on poultry productivity and gut health, the fundamemntal mechanisms associated with heat stress responses and intestinal barrier function are still not well defined. The aim of the present study was, therefore, to determine the effects of acute (2 h) heat stress on growth performance, gut integrity, and intestinal expression of heat shock and tight junction proteins in slow- (broilers of the 1950's, ACRB), moderate- (broilers of 1990's, 95RAN), rapid-(modern broilers, MRB) growing birds, and their ancestor wild jungle fowl (JF). Heat stress exposure significantly increased the core body temperature of 95RAN and MRB chickens by ~0.5–1°C, but not that of JF and ACRB compared to their counterparts maintained at thermoneutral conditions. Heat stress also depressed feed intake and increased serum fluorescein isothiocyanate-dextran (FITC-D) levels (P < 0.05) in modern broilers (95RAN and MRB) but not in JF and ACRB, indicating potential leaky gut syndrome. Molecular analyses showed that heat stress exposure significantly up regulated the duodenal expression of occludin (OCLN) and lipocalin (LCN2) in ACRB, zonula occludens (ZO-2), villin1 (VIL1), and calprotectin (CALPR) in 95 RAN, and only CALPR in MRB compared to their TN counterparts. In the jejunum however, heat stress down regulated the expression of PALS1-associated tight junction protein (PATJ) in ACRB, 95RAN, and MRB, and that of cadherin1 (CDH1) in MRB. In the ileum, heat stress significantly down regulated the expression of OCLN in 95 RAN, ZO-1 in MRB, gap junction protein alpha1 (GJA1) in JF, and VIL1 in ACRB compared to their TN counterparts. In summary, this is the first report, to our knowledge, showing that tight junction protein expression is environmental-, genotype-, and intestinal segment-dependent and identifying molecular signatures, such as CDH1, CALPR, and ZO-1, potentially involved in leaky gut syndrome-induced by heat stress in MRB.
Highlights
Poultry genetic selection for high growth rate and enhanced muscle development, driven by economic demand over the past 80 years, has made spectacular progress in term of breast yield, feed efficiency, and reduction of market age [1]
The broiler chickens involved in this trial were hatched from eggs collected at the University of Arkansas research farm and consist of four research lines; three of which represent the commercial broiler chicken of the 1950s (Athens Canadian Random Bred, ACRB) which is characterized by a slow-growth [26, 27], 1995 (95RAN) which is a moderate-growing line that has the genetics of 7 male and 6 female commercial broiler lines available in the mid-1990s [28], and 2015 modern random bred (MRB) which is composed of broiler packages offered by three broiler genetics companies and have been blended homogenously after many generations of random mating [29], and the fourth is the South East Asian jungle fowl, the wild-type ancestor (JF) [29]
(∼50 min to 1 h) after heat stress exposure, core body temperature of 95RAN and MRB chickens was significantly increased by ∼0.5–1◦C compared to their counterparts maintained at TN conditions (Figure 1C)
Summary
Poultry genetic selection for high growth rate and enhanced muscle development, driven by economic demand over the past 80 years, has made spectacular progress in term of breast yield, feed efficiency, and reduction of market age [1]. Compared to broiler of the 1950’s, a modern broiler of today achieves ∼400% increase in body weight arising mainly from breast muscle during 56 day period [2] These progresses make broiler (meat-type) chickens the most efficient and inexpensive food source [3] with a global world’s broiler meat production amounted to about 97.8 million metric tons in 2019 [4]. Unusual warm season and temperature anomalies have increased markedly in the past decades and are affecting biological systems including livestock animals, insects, and crops [9] Due to their high metabolic activity and lack of sweat glands, modern broilers are sensitive to heat stress. Koch and co-workers have shown that heat stress directly impairs gut integrity and disturbs the immune cell populations in bovine intestine [23]. The aim of the present study was, to determine the effects of acute heat stress on growth performance, blood FITC-D concentrations, and intestinal expression of heat shock and tight junction proteins in broilers of the 1950’s [26, 27], 1995 [28], 2015 [29], and their ancestor jungle fowl [29]
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