Individual periovulatory ovarian responses associated with pregnancy outcome following an Ovsynch protocol in Peranakan Ongole cows

Introduction Although ovulation synchronization protocols effectively control the timing of ovulation, pregnancy success remains highly variable among individual cows. The periovulatory ovarian responses associated with subsequent pregnancy outcome following synchronization remain poorly characterized in Bos indicus beef cattle. Therefore, this exploratory longitudinal study characterized individual ovarian sonographic and hormonal responses during an Ovsynch synchronization protocol and evaluated associations with pregnancy outcome in Peranakan Ongole cows. Methods Ten multiparous Peranakan Ongole cows without apparent reproductive abnormalities and body condition scores of 2.5–3.0 (5-point scale) were synchronized using a single Ovsynch protocol. Ovarian sonographic characteristics and circulating estradiol and progesterone concentrations were evaluated throughout the periovulatory period, and pregnancy was determined by ultrasonography. Results Nine of the ten cows ovulated following the synchronization protocol, and pregnancy was confirmed in four cows. Most post-ovulatory ovarian and hormonal variables showed weak associations at the 72-h post-ovulatory assessment. Baseline ovarian characteristics showed no detectable associations with post-ovulatory responses, whereas pre- and post-ovulatory estradiol concentrations remained positively associated. Among the post-ovulatory variables evaluated, corpus hemorrhagicum diameter showed the strongest nominal association with pregnancy outcome. Combining corpus hemorrhagicum diameter with largest follicle diameter or corpus hemorrhagicum echogenicity also showed nominal associations. Conclusion These preliminary findings suggest that early post-ovulatory ovarian characteristics, particularly corpus hemorrhagicum development, may be relevant to pregnancy outcome following synchronization.