Abstract. The present investigation was a part of a research project that aimed to study the reproductive and physiological traits of the rams as affected by selenium dietary supplementation and, housing heat radiation effect which is the change in animals perception of warmth between the different parts of the building or between indoors and outdoors of the farm measured by the difference in temperature-humidity index (THI) values.

To carry out such work, the animals were divided into four groups (A, B, C and E) of nearly equal average body weights and were raised in one shed, but divided to southern and northern parts. Two groups (A and B) were housed in the southern part of the farm (facing the bright sun day light), while the other two groups (C and D) were housed in the northern part of the farm (facing the cold air flow). One group in each part of the farm was kept without treatment as control (A or C) and the second (B or D) was treated with selenium (0.1 ppm/ kg dry matter [DM] of ration as sodium salenate) orally.

The results showed that dietary selenium supplementation improved significantly (P<0.01 or 0.05) most of the ram traits, during winter. Regarding the housing heat radiation effect, the results showed that the southern part was higher than the northern part of the farm with 0.8 THI unit and such change improved significantly (P<0.01 or 0.05) the ram traits, during winter. With regard to the interaction between the studied two factors, there were no significant effects except for the scrotal circumference and scrotal length which were high (P<0.01) in the rams supplemented with selenium and raised in the southern part of the farm, under the sub-tropical environment of Egypt.