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This study was conducted in the artificial insemination centre which located in Abu Ghraib / Baghdad/ Iraq from 1st October /2018 to April/2019 by using nine bulls at age between 2-8 years old and their weight between 600-800 kilograms from Holstein breed born in Iraq and have been trained for semen collection by artificial vagina method. The aim of study was to determine the optimal age for bulls used for artificial insemination and test their semens for insemination according to spccific indicators to achieve better pregnancy ratio possibly. The required investigations for semen evaluation involved colour, concentration , mass and individual movement as well as semen pH were implemented. The animals were divided based on their ages into three sub groups, 1st group from 2-4 years old , 2nd group from 4-6 years old and the 3rd group from 6-8 years under ideal conditions with respect to healthy conformation, feeding and heath management according to the Artificial insemination center. 72 ejaculations hadbeen collected over seven months by artificial vagina method at rate one ejaculation per bull weekly. The results of current study revealed that ejaculation volume in experimental bulls did not differ significantly(p>0.05) by differences of age categories which, 6.80 ±0.27 and 6.84 ± 0.60 ml for age category 6.38 0.37± amounted 2-4, 4-6 and 6-8 years old respectively. Regarding to mass movement of sperms, it was found positive marker in small age (39.26±1.66%) compared to middle age (33.04±2.46%) and old age (20.90±2.43%) with significant difference (p<0.01), moreover, there was a significant difference(p<0.05) between the middle and old ages and tend to be of middle age. Also, the individual movement of sperms was grater in small age (51.29±1.70%) compared to middle age (41.52±2.25%) and old age (29.77±2.83%) at significant difference (p<0.01) with signed difference(p<0.05) between middle and old age that tend to be to middle ages. With respect to sperm concentration there was in significant differences (P<0.01) of all age groups which Ponto lout the following results 1461.27±304.17, 1237.26±56.83 and 1558.53±432.04% for age grop 2-4, 4-6 and 6-8 years old respectively. Concerning semen pH, the results were showed that no significant differences(p<0.05) among of all age group that recorded the following results 6.60±0.02, 6.59±0.02 and 6.61±0.03% of ages 2-4, 4-6 and 6-8 years old respectively .The length of sperm head was high in old age (7.95±0.01) compared to middle age (7.16±0.02) and small age (7.09±0.03) with significant difference (p<0.01), also the width of sperm head recorded the significant difference(p<0.05) in favor of old age group (6-8) years old. The results showed that the elliptic form of sperm head was good in old age group (1.908 ± 0.010)µm compared with middle age group (1.772 ± 0.004) µm and small age group (1.778 ± 0.004)µm with significant difference (p <0.01). The elongation and regularity of the sperm head recorded a significant superiority(p<0.05) of the old group (6-8) years . in conclusion ,can be concluded that some semen characteristics were optimum in middle ages group and tend to be in favorable in this age groups ,so that the age exact positive and negative effect on characteristic of semen.