Date of Graduation

5-2026

Document Type

Thesis

Degree Name

Bachelor of Science in Agriculture

Degree Level

Undergraduate

Department

Poultry Science

Advisor/Mentor

Gisela, Erf

Committee Member

Beck, Chrysta

Second Committee Member

Orlowski-Workman, Sara

Third Committee Member

Santamaria, Jossie

Abstract

Heat stress (HS) is one of the most significant environmental stressors impacting poultry production worldwide, reducing growth, feed efficiency, welfare, and immune competence. With global temperatures rising, understanding physiological and immunological adaptations to HS is essential for sustainable production. Broiler chickens selectively bred for low water conversion ratio (LWCR) have shown potential for reduced water consumption under environmental challenges; however, their immune resilience under HS conditions compared with modern random-bred (MRB) broilers remains unclear. This study investigated the effects of cyclic HS on red- (RBC) and white- (WBC) blood cells and humoral immunity in LWCR and MRB broilers. Birds were reared under thermoneutral (TN; 24 °C) or cyclic HS (36 °C for 8 h daily from 29-42 days of age) conditions. At 42 days of age, blood samples were collected to determine the concentrations of RBCs, total WBCs, and various WBC populations (i.e., heterophils, monocytes, B lymphocytes, and T lymphocyte subsets such asCD4⁺, CD8⁺, and γδ T cells), as well as the concentrations of total IgM, IgG, and IgA antibodies in the plasma. WBC population analyses were conducted by flow cytometry after immunofluorescent staining of whole blood cell suspensions, and enzyme-linked immunosorbent assays (ELISA) were used to determine antibody concentration. In both LWCR and MRB lines, cyclic HS significantly (P ≤ 0.05) reduced the concentration of RBCs, total WBCs, total lymphocytes, B cells, total T cells, and heterophils, while the concentrations of monocytes were not affected. Additionally, concentrations of CD4+ T cells were higher in LWCR than MRB chickens kept at TN temperatures and dropped only in LWCR chickens due to HS, whereas no effects of line or temperature were observed for CD8+ T cells and concentrations of γδ T cells were overall lower in HS than TN conditions and in LWCR compared to MRB chickens. In both LWCR and MRB lines, plasma IgG concentrations were lower under HS, suggesting suppressed adaptive immune activity, whereas IgM- and IgA-concentrations were not affected by HS. Moreover, there were no line differences in circulating levels of IgM, IgG and IgA antibodies. LWCR broilers exhibited higher CD4:CD8 ratios and trends toward greater plasma IgA levels than MRB birds, suggesting a more balanced immune response under stress. Overall, these findings indicate that cyclic HS suppresses both cellular and humoral immunity. Genetic selection for water-use efficiency did not impair the ability of broilers to cope with HS and may provide partial immunological resilience. This work contributes to understanding how selection for resource efficiency influences immune adaptation and highlights potential genetic strategies for improving broiler performance and health in increasingly heat-stressed production environments.

Keywords

broilers; cyclic heat stress; blood leukocyte profiles; antibody concentrations; water efficiency

Additional Files
Thesis Final-Janski.pdf (738 kB)
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