ABSTRACT
This study aimed to investigate the relationship between increases in the luteinizing hormone (LH) profiles in the serum and vaginal mucus of cows induced by gonadotropin-releasing hormone (GnRH). Samples for LH determination were collected from Japanese Black beef cows during estrus, which was induced with a controlled internal progesterone-releasing device and the administration of cloprostenol immediately before GnRH administration and every 30â¯min from the start of GnRH administration until 6.5â¯h. The peak serum LH concentration was clearly identified at 2.5â¯h post-GnRH administration, with serum concentrations returning to near-pre-GnRH-administration values after 6.5â¯h, whereas the peak vaginal mucus LH concentration was identified 4.5â¯h after GnRH administration. These results indicate that the LH secretion peak in vaginal mucus appeared about 2â¯h after peak LH secretion in the serum.