This study was conducted to demonstrate the physiological responses of domestic ruminants to climatic challenges with special reference to temperature humidity index (THI) under environmental conditions of Egypt. The study involved 15 governorates: 6 in the Nile Delta, 7 in the Nile Valley, and 2 out of the Nile Valley. Monthly visits were carried out during the period extending from 2010 to 2022. The data was collected and analyzed by a research team belonging to Animal Production Research Institute and Central Laboratory for Agricultural Climate Institute, Agriculture Research Center. Respiration rate (RR, r/min), rectal temperature (RT °C) and Hematological parameters including Hematocrit value (Ht %) for buffaloes and cows, while goats and sheep respiration rate RR (r/min) was only recorded. The temperature humidity index (THI) was calculated by the meteorological data (air temperature AT°C and relative humidity RH %) in the entire region. The main objective of this study was to; Pout description of the climate of Egypt. Assess the physiological performance of domestic ruminants with regard to climatic challenges under the environmental conditions of Egypt. Suggest of recommendations for ruminants with different levels of THI characteristic of different regions under study were presented, this included the major required modification in nutrition, housing, or both to increase animal productivity or maintain it.Temperature humidity index (THI) is still the best indicator for ruminant performance under the environmental conditions of Egypt. It is not fair to evaluate that performance using the global THI. In Egypt, the expected THI trend towards 2050 includes Mild and moderate heat stress, it is expected that Mild heat stress could be interrupted by waves from cold waves and thermo-neutral. The moderate heat stress is expected to be interrupted by waves from Heat stress, Severe and Very severe heat stress especially during the months characterized by high relative humidity. Cows were highly sensitive to any change in micro-environmental conditions. Buffalo had the lowest RR under all levels of the THI. Buffalo and goats were sensitive to cold waves. Otherwise, cows and sheep were sensitive to heat waves. It has been concluded that it is not fair to evaluate the performance of domestic ruminants using the global THI. Buffalo and goats are efficient under conditions of climatic changes. Further adaptation studies for buffalo and goat are needed.