The present study is the first, to the best of our knowledge which demonstrate the physical and reproductive criteria for selection of Sahiwal sires to be used in Al. Although the artificial insemination (AT) is being practiced in Pakistan for the last 3-4 decades, however, no significant improvement in milk production has taken place in Sahiwal cattle. Perhaps one of the reasons that Sahiwal bulls used as AT sires were not screened through standard reproductive and productive criteria. Therefore the objectives of the present study were (1) to develop the standards of body weight and scrotal circumference (2) to determine the number of pixels of testes through Ultrasonography from birth until >100 months of age and (3) to develop standards for semen characteristics (volume, motility, concentration, morphology, plasma membrane and acrosome integrity) from puberty until 60 months of age in Sahiwal bulls. This study was carried out at following locations: LES Jhangirabad District Khanewal, SPU Qadirabad
District Sahiwal. The study was based on 128 Sahiwal bulls of different age groups (from o to >100 months of age). Bulls were evaluated for scrotal circumference (SC), body weight (BW) and number of pixels of testicular ultrasonograms (NP). Semen was evaluated once a week for 5 consecutive weeks from regularly donor bulls (n = 86) ranging in age from 25-30 to >100 mo. Semen volume, motility, concentration, morphology, percent live sperms, plasma membrane integrity (PMI) and normal acrosome (NAR) were compared between different age groups. Mean SC and BW increased (P<0.05) in a curvilinear manner from birth to >100 mo of age. Mean NP of testicular ultrasonograms increased (P<0.05) from 0 to 24 mo and then plateaued until
>100 mo of age. Body weight, SC, and NP were positively correlated with age from birth until >100 mo (r = 0.91, 0.87, 0.40 respectively). Ejaculate volume (5.7 ± 0.2 vs. 4.6 ± 0.09 ml) and sperm concentration (1281.6 ± 17.7 vs. 1115.8 ± 55.9 x 06/ml) increased (P<0.05) in mature bulls compared to younger ones. However, motility (68.6 ± 0.3%), plasma membrane integrity (50.8 ± 1.0%) and normal acrosome (74.8 ± 0.5%) remained insignificant due to age. In six of eight age groups studied morphological abnormalities were well within the range (18.1 ± 0.3%). In conclusion the BW, SC and NP of testicular ultrasonograms, ejaculate volume and concentration increased with age, moreover, semen quality is fairly independent of age except volume and concentration in Sahiwal bulls. These standards could serve as criteria for selecting young bulls as AT sires.