Effect of simultaneous administration of PGF2α and GnRH on follicular development, oestrus and the timing of ovulation in cows

The aim of this study was synchronization of oestrus in cows by simultaneous administration of PGF(2)alpha and GnRH. Synchronization of oestrus was repeated in 5 cows housed at our department of the university (group I) and 32 cycling cows in dairy farms (group II and III). In total 15 synchronized sexual cycles were observed in group I. Oestrus was synchronized by intramuscular administration of 500 mug of cloprostenol (Oestrophan, Ferring-Leviva, Prague, Czech Republic) and 100 mug of lecirelin pro toto (Supergestran, Ferring-Leciva. Prague, Czech Republic) at the same time during the luteal phase of the sexual cycle. The cows were examined by transrectal ultrasonography daily from the day of treatment to occurrence of a new luteal phase, and ovarian structures were evaluated in group I. Ultrasonographical examination of ovarian structures were performed on the day of treatment (day 0) and on days 3, 7 and 14 and samples of peripheral blood for progesterone determination by ELISA were obtained on days 0, 3 and 7 in group II (n = 12). Daily detection of oestrus and ultrasonographical examination on days 0, 14 and 28 after treatment were performed in group III (n = 20). The cows in oestrus were inseminated and conception rate was evaluated in this group. The new follicular wave occurred on the day 3 or 4 in all synchronized sexual cycles and ovulation occurred in 1 synchronized cycle on the day 3, in 6 cycles between days 7 and 9 and in 6 cycles between days 10 and 17 in group I. Ovulation did not occur and luteal cysts developed in 2 synchronized cycles in group I. Ovulation occurred in 5 cows until day 3 and in 4 cows between days 3 and 14 after treatment in group II. Ovulation was not proved in 3 cows until day 14 and luteal cysts developed in 1 of them. Total concentration of progesterone were 2.40 +/- 0.989, 0.22 +/- 0.054 and 0.44 +/- 0.323 ng/ml on days 0, 3 and 7, respectively. Oestrus occurred most frequently between days 3 and 8 after treatment and total conception rate after insemination was 41 % in group III. Simultaneous administration of PGF(2)alpha and GnRH during the luteal phase of the sexual cycle does not represent a sufficiently efficient method of synchronization of oestrus in cows. The majority of oestrus and ovulation occurs on days 3 and 8 after treatment.