The study aimed to deepen knowledge about anatomical and physiological features related to body heat loss ability and relation to semen quality of naturalized sheep Morada Nova and Santa Ines on tropical environment. Nine male Santa Inês and seven Morada Nova breed were subjected to two experiments. The first test included monitoring of coat features (amount of melanin, thick, length and diameter of the fibers), sweat rate, physiological indicators of thermal comfort (respiratory rate, heart rate, rectal temperature, surface temperature, skin temperature and scrotal surface temperature), sperm quality (sperm concentration, progressive motility, plasma membrane integrity, major defects, minor defects and total defects) and testicular parenchyma integrity coupled with the meteorological variables measured throughout the year. Statistical analysis was performed using the GLM and LSMEANS procedures of SAS software, version 9.1.3. Significant differences (P <0.05) were observed between the summer and fall and winter, with increase in termolitics parameters during the hot season. Already sperm quality did not vary throughout the year. The second experiment evaluated the capacity of rams to maintain body and testicular homeothermy under thermal challenge. Animals were subjected to heat tolerance test, which consists maintenance in the shade (period 1), followed by exposure to the sun (period 2) and return to the shadow (period 3). In the three periods were measured: respiratory rate, heart rate, body surface temperature, back, eyeball and scrotum, by infrared thermography. Adaptability of the animals was measured by heat tolerance index calculation. Sperm quality and testicular parenchyma integrity were evaluated before and after the heat challenge. In Period 1, the variables had baseline values for both genotypes. In Period 2, the variables involved in thermolysis significantly increased (P<0.05), which matches a thermal discomfort situation. In Period 3, the variables returned to baseline values and some values were lower than those in Period 1. Seminal and ultrasonographic variables did not share with thermal insult. It is concluded that MN and SIN rams had efficient thermolytic mechanisms that favor preserving gonadal functionality. The animals were considered resilient to a thermal challenge.
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