Kisspeptin stimulates LH secretion but not ovulation in mares during vernal transition

Managing the return to regular cyclicity after the winter anestrous period in the mare has been a challenge for the equine breeding industry. Specifically, efforts have been made to shift or shorten the vernal transition period and to have it followed by a predictable first ovulation at the commencement of the breeding season. Intravenous administration of kisspeptin is known to stimulate an LH response in both reproductively active and inactive mares. This study examined the effects of a constant rate infusion (CRI) of kisspeptin on mares during vernal transition. Mares were given a 30 hours infusion of kisspeptin at a low and high rate (66 nmol [88 μg] and 100 nmol [130 μg] per hour, respectively) or saline, and the LH and follicular response tracked. Plasma samples were collected every 15 minutes for the first 6 hours to determine if there is an acute effect of kisspeptin infusion on LH secretion. Plasma samples were then collected every 3 hours for a total of 72 hours to examine the ability of kisspeptin to stimulate an LH surge. A CRI of kisspeptin increased LH secretion in these mares but was not able to stimulate an LH surge. To examine the effect of kisspeptin on ovarian activity, follicular measurements were collected ultrasonographically until ovulation occurred or the follicles regressed. CRI of kisspeptin at these rates was unable to induce ovulation earlier than controls.