Date of Graduation

8-2025

Document Type

Thesis

Degree Name

Master of Science in Poultry Science (MS)

Degree Level

Graduate

Department

Poultry Science

Advisor/Mentor

Dridi, Sami

Committee Member

Alrubaye, Adnan

Second Committee Member

Looper, Michael

Third Committee Member

Orlowski, Sara

Keywords

chicken; heat stress; lipid metabolism; liver

Abstract

Heat stress (HS) is one of the most critical environmental challenges negatively impacting global poultry production, significantly compromising broiler performance, welfare, and economic viability. Specifically, heat stress profoundly disrupts physiological and metabolic processes, including hepatic lipid metabolism. Two broiler lines were divergently selected for high (HWE) or low (LWE) water efficiency. Heat-stressed HWE birds showed reduced fat content compared to their LWE counterparts, and HS reduced abdominal fat content in both lines. The purpose of this study was to determine the difference in underlying molecular mechanisms involved in this divergent fat content between the lines. Day-old chicks were placed in 12 environmentally controlled chambers (2 pens/chamber, 20 birds/pen). On day 29, daily cyclic heat stress (36°C, 9h/day) was applied to half of the chambers, while the others remained at 25°C, in a 2x2 factorial design. On day 49, liver samples were collected for lipid metabolism-associated gene and protein expression analyses. Data were analyzed by Two-Way ANOVA and Tukey’s HSD test using Graph Pad Prism. Data are expressed as mean ± SEM and were considered significant at P≤0.05. HWE birds exhibited higher fatty acid synthase FASN protein levels under thermoneutral (TN) conditions (P=0.0011), with both lines showing decreased FASN protein levels under HS. Malic enzyme (ME) protein expression was also significantly higher in HWE compared to LWE birds under both TN and HS conditions. LWE birds showed higher ATP citrate lyase (ACLY) gene expression under HS. The findings of this study showed that the main transcription factors are also upregulated, suggesting whether there is other main lipogenic protein effectors or high hepatic lipolysis rate in HWE birds that merit further in-depth investigations.

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