The scrotal temperature and its sectorial caloric gradient and physiologycal performance as the respiratory index, rectal and epidermal temperature were studied in six Fleckvieh bulls (age 26 to 30 months) to establish the influence of daily THI during summer time. Sectorial scrotal temperature changed across daytime (P < 0.001) when THI increased from 78.9 in the morning to 87.46 at middle day (P < 0.001). Rectal temperature were 38.45 ± 0.24 (morning), 39.20 ± 0.21(middle day) and 38.87 ± 0.24°C (afternoon) and respiratory frequency were 42.67 ± 7.45, 68.67 ± 5.89 and 60.33 ± 3.27 breaths per minute (P < 0.001) across daytime (P < 0.001); confirming the physiologycal alterations by heat stress. Sectorial scrotal – testicular axis showed different temperatures across daytime in the base (P < 0.01), pampiniforme cone (P < 0.05), cranial zone of epididimus (P < 0.10), testicular body (P < 0.10) and at tail of epididimus (P < 0.05); indicating that sectorial scrotal hetherotermy was modified. Maximun thermal scrotal gradient were -7.18 (am), -6.60 (md) and -7.60°C (pm). Radiant caloric flux across daytime were -2.715 (am), 0.260 (md) and -1.249 kcal/h (pm) and convective caloric flux were -0.265 (am), 0.116 (md) and -0.225 kcal/h (pm). Thermal scrotal transition from morning to middle day showed the sectorial caloric overload of +1.65°C (scrotal base), +1.28°C (pampiniforme cone), +1.02°C (head of epididimus), +1.0°C (testis) and +1.33°C (tail of epididimus). Scrotum around testis showed the smallest thermal alteration; however, the base and pampiniforme cone were thermally most altered. The highest daily THI was correlated to thermal alteration, passive thermolitic reduction and hyperthermy in the scrotum and testis; representing thermal and biochemical risks for testis’s physiology, local endocrine process, spermatogenesis and fertility in Fleckvieh bulls under daily heat stress in the tropics.