Abstract
Background: Thermal stress is a challenge in broiler production, impairing growth performance, physiological stability, and intestinal barrier integrity. Heat shock protein 70 (HSP70) reflects cellular stress responses, whereas zonula occludens-1 (ZO-1) is a tight junction protein involved in epithelial barrier maintenance. This study investigated growth performance, health status, physiological parameters, HSP70 and ZO-1 mRNA expression, and intestinal epithelial ultrastructure in broilers maintained under control, heat-stress, and cold-stress conditions.
Methods: A total of 150 21-day-old broilers were divided into control, heat stress (36 ± 1 °C), and cold stress (15 ± 1 °C) groups, with 50 birds per group. Thermal stress was applied continuously from day 21 to day 35. Each group was maintained in a single controlled room/mini-field unit without pen-level or independent chamber-level replication. Feed intake, body weight gain, feed conversion ratio (FCR), mortality, clinical signs, rectal temperature, and respiratory rate were recorded. Intestinal samples were collected for HSP70 and ZO-1 mRNA expression analysis and transmission electron microscopy (TEM). For qPCR, five birds per group were analyzed in duplicate. For TEM, five birds per group were examined, with four images/fields per bird. qPCR and TEM data were interpreted as biological observations within each condition rather than independent environmental treatment replicates.
Results: Heat-stressed birds showed reduced feed intake and body weight gain, impaired FCR, the highest mortality, rectal temperature, and respiratory rate, and pronounced intestinal epithelial ultrastructural alterations. Cold-stressed birds showed increased feed intake but reduced weight gain and impaired FCR compared with controls. HSP70 mRNA expression was higher in heat- and cold-stressed birds, whereas ZO-1 mRNA expression was lower, with the most pronounced changes in heat-stressed birds. TEM showed preserved epithelial structure in controls, moderate alterations under cold stress, and marked epithelial ultrastructural alterations under heat stress.
Conclusion: These findings suggest adverse thermal conditions were associated with inverse HSP70/ZO-1 mRNA expression pattern and ultrastructural epithelial alterations, suggesting inferred barrier-related epithelial alteration rather than direct evidence of functional barrier dysfunction, protein-level changes, or causality between HSP70 and ZO-1. Because each condition was represented by a single environmental unit, findings should be interpreted as biological response patterns under these conditions.