Investigation of the Effect of Different Hormone Applications on Pregnancy Rates in Repeat Breeder Cows

The current study aimed to investigate the effects of GnRH during insemination and progesterone administration on conception on the fourth- and fifth days following insemination in Repeat Breeder (RB) cows. The study included 40 Holstein breed RB cows housed under identical care and feeding circumstances. The animals were divided into four groups: group I (GnRH administered immediately after insemination), group II (GnRH administered immediately after insemination + progesterone administered on days 4 and 5 after insemination), group III (progesterone administered on days 4 and 5 after insemination), and group IV (control). All animals in the study had their ovulation checked at the 24th and 36th hours after insemination, and the pregnancy was examined by USG on the 45th day. The initial estrus of non-pregnant animals and their days were established. The ovulation rates at the 24th hour was 70% in group I, 90% in group II, 50% in group III, and 50% in group IV, whereas in the 36th hour they were 30% in group I, 10% in group II, 50% in group III, and 50% in group IV, respectively. The pregnancy rates were 70% in group I, 80% in group II, 60% in group III, and 30% in group IV. The untreated control group had lower pregnancy rates (p < 0.05) compared to the treatment groups. As a result, higher pregnancy rates were seen in the treatment groups compared to the control group, indicating that three distinct treatments can be used to increase pregnancy rates in RB cows.