Effects of heat stress on hypothalamic and pituitary mRNA expression in broilers

Authors: BECKFORD, RONIQUE - University Of Maryland; FARLEY, LINDA - University Of Maryland; ELLESTAD, LAURA - University Of Georgia; Proszkowiec-Weglarz, Monika; BRADY, KRISTEN - University Of Maryland; PORTER, TOM - University Of Maryland

Submitted to: Poultry Science Association Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 5/14/2018
Publication Date: 9/1/2018
Citation: Beckford, R.C., Farley, L., Ellestad, L.E., Proszkowiec-Wegla, M.K., Brady, K., Porter, T.E. 2018. Effects of heat stress on hypothalamic and pituitary mRNA expression in broilers. Poultry Science Association Meeting Abstract. 97:220.

Interpretive Summary:

Technical Abstract: Heat stress in chickens occurs when the ambient temperature rises above the thermoneutral temperature and birds are unable to efficiently reduce their body heat. Effects of heat stress on broiler production include increased mortality rate in the flock and decreased performance by the birds that survive. Identifying a management strategy that reduces the negative consequences of heat stress and that is not labor intensive or costly would be beneficial. To effectively evaluate these strategies, it is important to measure not only production parameters but also the underlying physiological mechanisms. The hypothalamus and pituitary regulate metabolism and stress responses. Therefore, the objective of this study was to evaluate corticotropic and thyrotropic mRNA expression in the hypothalamus and pituitary of broiler chickens subjected to heat stress. At 24 days of age, Ross 708 male chickens were placed into battery cages in 8 grower batteries in each of 2 rooms maintained at 22ºC (10 birds/cage, 2 cages/battery). On d 31, four batteries from each room were moved into two rooms with an elevated ambient temperature (35ºC) for 8h for the heat stress challenge (HS). Remaining batteries stayed in the two thermoneutral rooms with an ambient temperature of 22ºC (no heat stress; NHS). After the 8h heat stress challenge, birds were euthanized and hypothalamus and pituitary samples collected from 16 birds per treatment (2 birds/cage/battery/room), flash frozen and stored at -80o C until RNA extraction. Reverse transcription qPCR was used to compare mRNA levels between HS and NHS birds. Differences in expression were determined using mixed model ANOVA (SAS v9.4, Cary NC) to compare mRNA levels of each target gene normalized to PGK1 and GAPDH (n=16/treatment) mRNA levels in the pituitary and hypothalamus respectively. In the adrenocorticotropic axis, expression of pituitary corticotropin-releasing hormone receptor 1 was significantly downregulated (P < 0.001) while corticotropin-releasing hormone receptor 2 was 2-fold higher (P=0.001) in the HS birds. Interestingly, pituitary mRNA levels for proopiomelanocortin were not significantly (P > 0.05) different. In the thyrotropic axis, heat stress increased the expression of metabolic related genes. Both thyroid hormone receptor ß (P=0.01) (2.8-fold) and thyroid stimulating hormone ß (P=0.009) (1.4-fold) were higher in HS than NHS birds. Heat stressed birds respond with a myriad of molecular events, and this study provides insight into the events occurring within the hypothalamus and pituitary. Understanding these pathways and their regulation during heat stress will enable researchers to better evaluate management strategies to combat heat stress.