|Ph.D Thesis||Department of Biology|
|Assoc. Prof. Arad Zeev|
|Prof. Emeritus Gershon David|
It is well established that elevated temperature causes mortality, morbidity and other deleterious effects on the productive performance of commercial layer hens. The survival time of mature chickens under high ambient temperatures depends on their ability to regulate the rate of increase of body temperature. The cellular heat shock response is characterized by a selective expression of heat shock proteins (HSPs). This enables the development of a specific reaction through which the cell confronts short lasting changes in ambient temperature. The basic aims of this study were:
A. To study whether a single heat exposure during the embryonic or postnatal development can result in “thermal immunity” at maturity and whether this involves HSPs. B. To explore the in vivo kinetics of the cellular heat shock response. The results indicate that embryonic heat exposure improves the constitutive levels of HSPs, the cellular heat shock response, and the recovery of the reproductive system after an additional heat shock at maturity. Survival time was improved as a result of postnatal heat exposure. In the three groups examined, the on-line experiments revealed a gradual pattern of body temperature regulation and of HSP expression. The regulation of the cellular heat shock response was found to be tissue-dependent. The findings in this study show that heat resistance in mature fowls can be achieved by a single heat exposure at early developmental stages. The heat resistance results in a delayed dependence on HSPs as a major defense mechanism. This improvement is associated with an improvement in productivity and is manifested by a more effective regulation of body temperature.