Abstract
The study was conducted to investigate the effect of addition of zinc sulphate, cysteine, Prostaglandin F2α (PGF2α) and their combination to the diluted semen on semen characteristics of Holstein bulls after different periods of cooling. The study was conducted on Artificial insemination Center/ Directorate of Animal Resources/ Ministry of Agriculture at Abu-Graib at the west of Baghdad during the period of Aug. 2019 to the Dec. 2019. Seven Holstein bulls were used, Aged between 2.5- 3 years. Semen was collected via Artificial Vagina one ejaculate per a week for three months. Fresh semen was evaluated which were of bad grand pooled semen were divided into 5 parts. The first part (T1) only diluted semen (Tris) serve as a control. The 2nd part (T2) added 0.576 mmol/ ml of zinc sulphate to diluted semen. The 3rd part (T3) added 5 mmol/ ml of cysteine to diluted semen. The 4th part (T4) added 37.5 pg/ ml of PGF2α to diluted semen to diluted semen. The 5th part (T5) added a combination of previous components to the diluted semen. Then the semen evaluated at 5C° after 24, 48 and 72 hrs. The results showed that the addition of zinc sulphate on cooled diluted semen have no significant difference between different periods in the percent of sperm individual motility. Addition of zinc sulphate and cysteine showed a significant increase (P<0.05) in the percent of sperm liveability. The addition of a combination (zn sulphate, cysteine and PGF2α) showed a significant decrease (P<0.05) in sperm abnormalities percent especially at 5C°. The results also showed the addition of zinc sulphate and PGF2α increase the percent of HOST (Hypo-osmotic swelling test) of spermatozoa at 48 hrs. after cooling. zinc sulphate addition showed a significant increase (P<0.05) at 5C° during as comported with other cooled period in the HOST. The addition of zinc sulphate showed a significant increase in cell membrane integrity at 5C° cooled semen. It was concluded that addition of antioxidant and hormone might improve semen quality of Holstein bulls.

Key words: Zn, Cysteine, PGF2α, cooled semen, in vitro, Holstein bulls.