This research aims to check the impact of climatic variability of the THI index during the three main seasons of the year in Egypt on growth traits and biochemical blood components in native bovine calves. Eighteen Egyptian bovine calves after weaning were used in this study. The experimental design included three experimental groups according to the year's seasons. In the 1st group, sex calves were rearing under winter conditions. In the 2nd group, sex calves were kept during the spring season. In the 3rd group, sex calves were maintained during the summer season. Weekly and monthly Temperature-humidity index (THI) was calculated for the three seasons. The daily body gain (DBG) the feed intake (DMI), and water consumption (WC) were measured weekly for each calf. The highest THI value (85.5) during summer resulted in a significant (P<0.01) decrease in DBG, daily DMI, thyroid hormonal levels, total proteins, and glucose and a significant (P<0.01) increase in daily WC and levels of cortisol and urea. The rate of decline increases with increasing THI values from low THI in winter (68.1) to moderate THI during spring (74.9) and high THI (85.5) during the summer season. With increasing THI, the depression in DBG was more than the decline in daily DMI; therefore, food conversion increases when the value of THI increases. THI has highly (P<0.01) significant negative correlations with DBG, DMI, thyroxin (T4), triiodothyronine (T3), total proteins, and glucose and has highly significant (P<0.01) positive correlations with water intake as well as cortisol and urea concentrations.