Effect of Short-Term and Prolonged Heat Stress on the Number of Hypothalamic Neurons (Gonadotropin Hormone Inhibitor) and Blood Parameters in Arbor Acres Broilers

Different stressors can affect the neuroendocrine system. Stressors mediate the function of hypothalamic-pituitary-gonadal axis through the activation of the sympathetic nervous pathway in the hypothalamus. The evidence has revealed that stress signaling can exert some disruptive effects in the brain, gonads, and other tissues. Regarding this, the present study was performed to investigate the role of thermal stress in neuroendocrine changes, gonadal system, and variations in metabolic rate. The current study was conducted on 21 female Arbor Acres broilers. The subjects were randomly divided into three groups of control (n=7) receiving the normal temperature, short-term thermal stress (n=7) being exposed to a temperature of 21°C rising to 21, 25, 29, and 33°C for 4 h, and long-term thermal stress (n=7) being exposed to a temperature rising from 21to 30°C, and then fixed at30°Cfor 4 weeks. After collecting blood samples, fixation was performed for brain sampling. The hypothalamic tissue sections were stained by immunohistochemistry, and the gonadotropin-inhibitory hormone (GnIH) neurons in the hypothalamus were counted. Furthermore, the concentrations of plasma metabolite (e.g., glucose and cholesterol) were measured for each of the birds. According to the results, cholesterol level showed a significant change after exposure to short- and long-term thermal stress. However, no significant change was observed in the glucose level. Additionally, the exposure to short- and long-term thermal stress resulted in a significant change in the number of the red blood cells, heterophil, and lymphocytes. Nonetheless, the results revealed no significant change in monocytes and total white blood cell count. Furthermore, the number of GnIH neurons in the broilers was not significant after the exposure to two types of thermal stress. As the findings of the present study indicated, thermal stress exerted a negative effect on blood parameters; however, it induced no change in the number of GnIH neurons. It is recommended to measure the effects of thermal stress on other metabolites and hormones

Keywords:

Thermal stress , GnIH neuron , Blood parameters , Broiler