Synchronization of estrus in cows using double PGF2α, GnRH-PGF2α and hCG-PGF2α combination

The aim of this study was to compare the effectiveness of treatments combining GnRH and PGF(2alpha) hCG and PGF(2alpha) combinations, and double PGF(2alpha) administration for synchronization of estrus in cows. This study was carried out in 30 Brown Swiss cows, aging 3 - 5 years. The cows were randomly divided into three groups. In group I (n = 10), the cows were treated with an intramuscular injection of 20 mug GnRH (day = 0) at a random stage of the estrous cycle followed by intramuscular injection of 0.150 mg PGF(2alpha) 7 days later (day = 7). In group 11 (n = 10), the cows were treated with an intravenous injection of 3000 IU hCG (day = 0) at a random stage of the estrous cycle followed by intramuscular injection of 0.150 mg PGF(2alpha) 7 days later (day = 7). In group III (n = 10), the cows were received two injections of 0.150 mg PGF(2alpha) 11 day apart (day = 0, and 11). GnRH (10 mug) was injected intramuscularly to the cows 48 hours after the injection of PGF(2alpha) in the groups I and 11, and after the second PGF(2alpha) in group III. The cows were inseminated 12 hours after the GnRH injections. Blood samples were collected daily to determine plasma progesterone levels for 13 days in the groups I and H, and for 15 days in the group III starting from the day of GnRH, hCG and first PGF(2alpha) injections respectively. The mean interval injections-estrus, injections-ovulation, synchronization and pregnancy rates of the groups were determined. Plasma progesterone levels on day 0 and at estrous were similar among the three groups, but it was significantly higher (p < 0.01) in the groups I and 11 than in the group III on the day of PGF(2alpha) administration. The mean GnRH injections-estrus and injections-ovulation interval in the groups 1, 11 and III were 52.2 +/- 1.69, 48.4 +/- 1.34 and 68.2 +/- 1.31 hours; 70.4 +/- 1.17, 67.3 +/- 1.36 and 90.6 +/- 2.15 hours, respectively and were significantly different (p < 0.01). The synchronization rates tend to be higher in the groups I and 11 (100 %) than in the group 111 (80 %), and pregnancy rates of the groups 1, 11 and III were 60 %, 60 % and 30 %, respectively. As a conclusion, application of a GnRH and hCG analogue prior to synchronization of estrus with an injection of PGF(2alpha) may provide better results than two injections of PGF(2alpha) for estrus synchronization in cows.