Comparative analysis of delayed ovulation and associated ovarian patterns in the Ongole crossbred cattle.

Background: Delayed ovulation can have harmful effects on cattle reproduction, especially in countries that rely on artificial insemination, resulting in significant economic losses, as evidenced by Indonesia. Aim: This study provides novel insights into hormone dynamics and ovarian environment comparisons in delayed ovulation (DO) and Normal cows (NO) cows. Methods: Eight Ongole-crossbred cows with DO or NO over four estrous cycles were observed. Daily ultrasonography was used to monitor dominant follicle size and corpus luteum (CL), while estrus behavior and blood sampling were used to record peripheral reproductive hormone patterns from 2 days before to 6 days after estrus onset. Statistical comparisons between the DO and NO groups were performed using the SPSS 26 software, with significance set at p < 0.05. Results: The results showed that DO cows had similar cycle durations but ovulated later than NO cows. Furthermore, DO cows had significantly smaller follicles (1.14 ± 0.2 cm) in the pre-estrus phase, larger follicles at estrus onset, and a larger CL during pre-estrus that should have regressed. Elevated progesterone levels (2.09 ± 0.34 ng/ml) before and after estrous treatment inhibited luteinizing hormone (LH) release, thereby delaying ovulation. DO cows exhibited lower LH levels and LH surges 2-4 days after the onset of estrus, altering the ovarian environment and hindering oocyte maturation. Conclusion: Delayed ovulation in cows is associated with hormonal and ovarian changes that reduce fertility, highlighting the need for further research on progesterone and hypothalamic-pituitary regulation to develop targeted fertility improvement strategies.