New strategies to improve the efficiency of the ovsynch protocol in primiparous dairy cows

The aim of this study was to create new strategies to increase the pregnancy rate in "ovsynch protocol" treatment. Two programs for synchronisation of ovulation and for synchronisation of ovulation and oestrus, similar to the ovsynch, were developed for the use in lactating primiparous dairy cows. Lactating Holstein-Friesian cows were randomly divided into five treatment groups: the GPG group (ovsynch) was treated with GnRH on day 0, PGF (PGF2 alpha) on day 7, and received the second dose of GnRH 48 h later; the groups -7PGPG and 2- PGPG received the same treatment as the GPG group, but were given an additional injection of PGF 7 and 2 d before the start of the GPG treatment; respectively, the PG9PG group received the same treatment as the -2PGPG group, with the modification that the first GnRH injection was given simultaneously with the first PGF on the 2(nd) d; the GPEG group received the same treatment as the GPG group, but was injected an additional oestradiol propionate (EP) 24 h after the PGF. Plasma progesterone concentrations were determined at the days of the first hormone injection and the last PGF injection. Ovulation rates after the first GnRH and last PGF injections were calculated and presumptive sizes of the follicles on the last PGF injection day were determined in all the cows by rectal palpation. Cows detected to be at oestrus in 72 It after the last PGF injection was inseminated between the 8(th) and 12(th) h of their oestrus. Cows not detected to be in oestrus by 72 It after the last PGF received timed artificial insemination (TAI). While the ovulations mostly occurred in the GPG, GPEG, and -7PGPG groups at a period between the 48(th) and 96(th) h after the last PGF injection, the ovulations had shifted and occurred between 72 and 120 h, with 66.7% of all ovulations recorded between 72 and 96 It in the -2PGPG group. In the PG9PG group, ovulations took place dispersedly between the 0(th) and 120(th) h after the last PGF injection. The pre-synchronisation treatment (-7PGPG) by a PGF injection 7 d prior to the ovsynch protocol did not enhance the ovulation or pregnancy rates. The pre-synchronisation treatment by PGF injected 2 d before the ovsynch protocol, increased the number of cows that ovulated after the first GnRH injection (88.9% vs. 38.9% P 0.05). Adding EP to GPG (GPEG), enhanced the expression of oestrus (P 0.05). In conclusion, the -2PGPG and GPEG treatments are potentially new methods for routine synchronisation of ovulation and oestrus and/or ovulation, respectively, in primiparous Holstein-Friesian cows