Heat along with high humidity is one of the causes of impaired milk production and fertility of cattle, especially in the summer or in tropical and semitropical regions. Such problems can be aggravated with the prospect of global warming. In the hottest regions of Brazil there is a preference for crossbred Holstein (H) X zebu (Z), mainly Gir (G) cattle that form the Girolando synthetic breed whose composition is mainly ⅝ GxH. Girolando animals are more tolerant to heat than breeds of European origin, such as the Holstein. However, even these animals are sensitive to intensive heat, with great variability in their thermotolerance. To cope with the effects of excessive heat on the fertility and consequent productivity of these animals, which can be potentiated by possible climatic changes, this project evaluates Girolando cows with ¼ to ⅞ GxH breed proportion under high conditions of temperature and humidity. From the determination of the temperature and humidity index (THI), procedures are carried out in order to identify genomic markers such as Quantitative Trait Loci (QTL) or single site polymorphisms (SNP) associated with improved thermoregulation, estimated by the regulation of body temperature, and the developmental competence of the oocyte. In addition, the project aims to evaluate alternatives to reduce the effects of thermal stress, by means of feeding or hormonal manipulation of estrous cycle so that recommendations of mitigation procedures can be adopted in the short term. In this way, two fronts for mitigation are expected, as follows: selection (medium-long term) and management recommendations (short-medium term). Other aspects studied are the molecular mechanisms (gene expression, protein profile and epigenetic pattern) involved in the thermal stress in oocytes, so that the results can also contribute to the proposition of new mitigation procedures in the female gamete. We hope to identify genomic regions associated with thermotolerance and oocyte fertility potential that can be used for selection in Girolando cows. It is also expected the development / optimization of a process to mitigate the effects of heat on production and reproduction, generating methodologies that can be applied to milk production systems in Brazil, making the activity more profitable, either through more efficient feeding or more effective insemination programs. Overall, the results are expected to contribute in the near future to minimize the negative effects of high temperature and humidity indexes on milk production and fertility.