COMPOUND 6, A SYNTHETIC KISSPEPTIN ANALOG, INCREASES PLASMA LUTEINIZING HORMONE CONCENTRATIONS IN BEEF COWS UNDER LOW CIRCULATING PROGESTERONE CONCENTRATIONS

Reproductive performance affects profitability in the food animal industry. Estrus synchronization has improved fertility, but hormonal tools like kisspeptin (KP) have potential for further enhancement. However, KP’s short half-life limits its use in cattle. Compound 6 (C6), a synthetic KP analog, was created to improve stability and extend half-life. While C6 has stimulated reproductive responses in other species, its ability to induce LH secretion and ovulation in cattle is less understood.

The study investigated the effects of C6 on plasma LH, serum progesterone (P4), and ovarian dynamics in cattle. Ten cows underwent two treatments: control (CON; 2 mL saline IM; n=10) or C6 (100 nmol in 2 mL saline IM; n=10). Estrus synchronization was achieved using prostaglandin F_2ɑ, GnRH, and internal progesterone-releasing devices (CIDR), with treatments on Day 6 of follicular wave emergence. With CIDRs in place to keep circulating P4 low, blood samples were collected hourly for 12 hours post-treatment to measure plasma LH. Additional blood samples for P4 analysis and ultrasonography of ovaries were collected at -1 and +11 hours, twice daily for four days post-treatment, and once daily thereafter for three days. C6 significantly increased plasma LH concentrations (p < 0.0001) compared to CON, especially at Hours 4, 5, and 6. Luteinizing hormone levels remained elevated (p < 0.0001) from Hours 4 to 7 in the C6 group. Serum P4 concentrations were higher in the CON group at baseline (p < 0.0078) and decreased significantly after CIDR removal (Hours 168, 192 and 216; p < 0.0001). C6 treatment led to a significant reduction in P4 at Hour 192 (p = 0.045). Ultrasonography did not show luteal tissue, but C6-treated cows were more likely (p < 0.0001) to lose a dominant follicle within 36 hours of treatment. Collectively, C6 caused an increase in plasma LH concentrations and possibly promoted ovarian follicular turnover. Further research is warranted to determine if the C6 induced increase in LH consistently promotes ovarian follicular turnover and the effectiveness of integrating C6 into bovine breeding programs as an alternative or supplement to GnRH-based synchronization.