RESUMO
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.
