الفهرس 
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Abstract
This work aimed to throw a light on the monthly and seasonal ariations in the concentrations of plasma testosterone hormone )efore and after ejaculations and plasma cortisol hormone levels. lso, it aimed to study the effect of ejaculations on the plasma :estosterone levels. The relations of testosterone and cortisol Levels, libido and semen picture were studied also in relation to ambient temperature, relative humidity and day light length.
This study was carried out on three mature native bulls. The semen samples were collected weekly for one year, two ejaculates /time by using the artificial vagina. Plasma samples were collected before and after ejaculations. Ambient temperature, relative humidity and day light length were measured in each day of semen and plasma samples collections.
Testosterone hormone levels were assessed in plasma samples collected before and after ejaculations, while cortisol hormone levels were assessed in plasma samples collected after ejaculations only. Both hormones were assessed by radioimmunoassay (RIA).
Libido index and reaction time were measured for each ejaculate. Semen samples were examined for: ejaculate volume, ejaculate pH, mass activity, individual sperm motility, sperm cell concentrations, alive sperm percentages, morphological sperm abnormalities, methylene blue reduction time (MBRT), initial.