The study was carried out in the animal house at the College of Veterinary Medicine/University of Tikrit for the period from January to July 2017, using 16 Awassi lambs at the age between10-12 months, and an average weight (36 kg). The animals were divided into four groups each one included four lambs. The first group was considered as control (T1), and kept without the addition of bread yeast to foods.The diets in the others groups (T2, T3 and, T4) contained the  yeast in the proportions of (3, 5 and, 7 g /animal / day), respectively. Wheat straw was introduced as a free coarse feed as well as concentrated feed at 2.5% of weight which is measured weekly for 75 days.
The aim of this study was to investigate the effect of several levels of dry bread yeast (Saccharomyces cerevisiae) on some productive, reproductive traits, and number of blood parameters. The results showed no significant differences for all studied traits (final weight, Body condition score, concentration of testosterone, blood glucose, protein and cholesterol). From all testicular and epididymis measurements were taken from animals after slaughter (weight and size of testicles, length and diameter of testis, weight of epididymis and length of one of them) the only testicular weight and size showed significant increases in all groups  were given bread yeast to foods and the group that given high levels of yeast (T4) appeared highest increases compared with other treated group (T2 and T3).
In conclusion, the present study demonstrates that the using of Saccharomyces cerevisiaeas supplementation in lambs feed leads to improvingthe reproductive performance in spite of insignificant changes in the production trait and blood parameters.