Intestinal gene expression in heat-stressed broilers selected for high water efficiency

The major goal of this study was to compare mRNA expression associated with water homeostasis in intestines of high water efficient (HWE) broilers to expression in unselected Modern Random Bred (MRB) broilers under thermoneutral (TN) and heat stress (HS) environments.

A 2 × 2 factorial study was conducted with two lines (MRB and HWE) and environments (TN and HS). Males were raised in environmental chambers and maintained in TN conditions from 0 to 4 weeks. From 4 to 7 weeks, broilers were maintained under TN conditions (25C) or exposed to cyclic HS conditions (35C, 8 h/d). At 7 weeks, upper and lower duodenum, and cecum samples were obtained. mRNA was determined by RT-PCR for; 1) heat shock proteins (HSP70, HSP90), 2) the arginine vasotocin (AVT), mesotocin (MT) and receptors (VR2, VR1a, VR1b, MTR), 3) the renin angiotensin system (RAS): angiotensinogen (AGT), angiotensin receptors, (AT1, AT2), renin (REN), AGT converting enzyme (ACE), and Na⁺/⁺ATPase (ATP1B1), 4) aquaporins (AQP1-5 and 11), and 5) tight junction proteins occludin (OCLN), and claudins (CLDN2, CLDN15).

A main effect of HS was observed for HSP70 and HSP90 expression in all three intestinal-segments. In lower duodenum, HS-induced upregulation of AVT was accompanied by elevations in VR2, VR1a, VRb, AT1, AQPs (1, 3, 11) OCLN, and CLND2, CLDN15. Main effects of broiler line were observed with HWE exhibiting increased mRNA expression of VR2, VR1a, VR1b, AQP1, AQP3 and AQP5 and CLDN2 in the upper duodenum. There was also higher VR2, MT and AQP5 and lower expression of CLDN15 in the lower duodenum but there were no differences in gene expression between MRB and HWE lines in the cecum. Heat stress upregulated AVT, VR1a, MTR, AVT/MT ratio, AQP1, and AQP3 but downregulated ACE in the upper duodenum. Heat stress also upregulated AVT, VR2, VR1a, VR1b, MTR, AT1, AT2 AQP3, ACP5, OCLN, CLDN2, CLDN15 in the lower duodenum and cecum.

The results provide insight into mechanisms responsible for water efficiency in HWE broilers and provide new information in gene expression in the gastrointestinal tract of broilers exposed to chronic cyclic heat stress conditions.