In order to determine different protocols of synchronization and their efficiency on pregnancy rate after fixed-timed AI (TAI), 120 dairy Holstein cows (n = 120) were assigned randomly to six groups: 1) two injections of Prostaglandin F2α (PGf2α) with 12 days apart as a control group, 2) two injections of Gonadotropin Releasing hormone (GnRH) with 9 days apart and an injection of PGf2α at day 7, 3) injection of GnRH and PGf2α with 7 days apart, then single injection of Estradiol Benzoate (EB) after 48 h, 4) injection of progesterone (P4) in conjugation with EB then after 7 days PGf2α injection and after 48 h an injection of GnRH were done, 5) as group 4 but EB was used instead of GnRH, 6)injections of PGf2α and EB conjugated with Human Chronic Gonadotrophin (hCG) with 12 h apart. Animals in group 1 (control), groups 2-5 and group 6 were inseminated after 72, 20 and 36 h, respectively. Serum P4 concentration of group 4 (4.43± 1.50 ng mL-1) was higher than control group (2.34±1.36 ng mL-1) at day 5 after insemination (p<0.05); P4 concentrations of groups 3 and 4 have significant differences with control group (2.69±2.64 and 2.56±1.40 versus 0.81±0.41 ng mL-1, respectively, p<0.05) at a day after second injection and groups 4 and 5 were in higher level of P4 concentration than control group at insemination time (3.14±1.9 and 2.89±1.8 versus 0.45±0.19 ng mL-1 respectively, p<0.05). Pregnancy rate were 0, 50, 45, 10, 30 and 45% for group 1 (control) through 6, respectively.
A. Karimi , H. Karami , M.M. Moini , A.A. Ahmadi Sefat and E. Haghvirdilu , 2007. Comparison Between Different Protocols of Synchronization and Their Efficiency on Pregnancy Rate of Dairy Cattle . Pakistan Journal of Biological Sciences, 10: 3557-3563.