The main objective of this study was to investigate the effects of different ambient temperatures {thermo-neutral (TN) or heat stress (HS) in 22 and 30 wks of age} and dietary supplementation of different selenium (Se) sources {inorganic (control group) at 0.1 mg/ kg diet, organic Se (Selenium Yeast) and Nano Se each at 0.3 mg/ kg diet} on sexual maturity, laying performance, egg quality, hatchability traits and physical semen quality, as well as some blood parameters and plasma constituents for Sinai hens during the early laying stage (22-34 wks). A total of 198 (180 females + 18 males) 22-wks-old of Sinai birds were used and randomly distributed into two experimental groups (TN & HS), and then each group was divided into three sub-groups (inorganic, organic and Nano Se) in a factorial design (2x3). At 17 to 20 wks of age, birds were fed pre-lay diet contained 2% Ca then, convert to layer diet until the end of experimental period (34 wks).
The results indicated that heat stress resulted in a significant decrease in 1st egg weight and age at sexual maturity, body weight and change in body weight, laying rate (%), egg number, egg weight, egg mass and feed intake per hen, live sperms (%) and hatchability (%). External and internal egg quality and fertility (%) were not significantly affected by heat stress. Also, heat stress significantly increased total embryonic mortality, dead and abnormal sperms in semen. Besides, lymphocytes (L) cells (%), plasma total protein, hemoglobin (Hb) concentration, white blood cells count, eosinophils cells (%), monocytes cells (%), globulin, albumin, calcium, phosphorus and TAOC were significantly decreased for hens reared under heat stress. Moreover, significant increases were recorded for total lipids, heat shock protein 70 for Sinai hens reared under heat stress than those reared under thermo- neutral during the studied laying period. Supplementing different selenium sources to the diet, especially Nano selenium had significantly improved all parameters under experimental conditions as compared with control diet. These results indicated that heat stress severely reduced productive and reproductive performance for Sinai hens, whereas the productive and reproductive performance was improved by dietary different Se sources (Nano and organic Se) supplementation at 0.3 mg/ kg under heat stress conditions, without any adverse effect on the vitality of hens.