Comparison between different protocols of synchronization and their efficiency on pregnancy rate of dairy cattle.

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 F(2alpha) (PG(f2alpha)) with 12 days apart as a control group, (2) two injections of Gonadotropin Releasing hormone (GnRH) with 9 days apart and an injection of PG(f2alpha) at day 7, (3) injection of GnRH and PG(f2alpha) 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 PG(f2alpha) 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 PG(f2alpha) 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.