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The role of heat shock proteins in the development of thermotolerance in broilers


Thermotolerance refers to the state of resistance to hyperthern iic conditions that can possibly be improved by acclimation. By definition, broiler acclimation to heat stress is an expression that describes the birds' increased capacity to survive to an exposure to high temperature. Increased thermotolerance by acclimation might be a key to maintain the productivity of broiler industry in tropical and subtropical countries during summer and to control the mortality that occurs during heat waves Despite achieving acceptable performance responses to acclimation in some studies with broilers, we found very little research in this area and no studies that use prehatching heat treatment to induce thermotolerance. Also, no elucidation for the mechanism involved in thermotolerance and acclimation is available. Stress causes a variety of alterations in cellular physiology including increased synthesis of highly conserved proteins known as heat shock protein (hsp). Among the hsps, the most prominent proteins induced either by heat or other factors, and showing a close correlation to the induction of tolerance to high temperatures belong to the hsp7 O family. The process also involves hsp9 O and hspI O4. Broilers submitted to heat stress exhibit overexpression of hsp7O, but no information on hsp9 O and hspI O4 synthesis in tissues of birds under stress is available. Heat shock proteins may exert regulatory effects on the action of a broad range of intracellular signaling system such as receptor binding protein. Thus, they affect hormone action and utilization, mainly steroid hormones. On the other hand, thermoregulation is under control of thyroid hormones. Therefore, in order to understand the principles of heat stress tolerance and acclimation, it is necessary to understand how single factors (hps, T3, T4or corticosteroids) interact with each other in a complex biological context. The main purpose of this project is to investigate the hsp expression induced by prehatch and neonatal treatment, and its significance in thermotolerance and acclimation of broilers by studing: 1. The expression of hsp (hsp7O, hsp9O) in different tissues (brain, liver, heart and muscle) and hormones (T3, T4and corticosteroids) in plasma of embryos and posthatch broilers chickens, according to the temperature treatment, the strain and the sex of the birds. 2. The conditions of incubation to achieve better thermotolerance (heat, cold, degree and duration of exposure to stress) without affecting hatchability, chick quality and/or first week posthatch survival. 3. The effect of embryo treatment upon performance and survival of broilers submitted to heat stress at about 6 to 7 weeks. (AU)

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