Changing the route of GnRH administration according to the initial cyclic phase of the Ovsynch protocol may optimize reproductive outcomes in dairy cows.

While the study did not find significant differences in fertility outcomes based on GnRH administration route, there were notable trends that suggest further research is needed to explore these relationships.

Summary and findings

This study investigated the effects of gonadotropin-releasing hormone (GnRH) analogues and administration routes on fertility outcomes in dairy cows subjected to the Ovsynch protocol. A total of 406 multiparous Holstein cows were assigned to receive either intramuscular or epidural GnRH treatments. No significant differences in pregnancy or pregnancy-loss rates were detected between treatment groups.

Abstract

Background This study aimed to investigate the effects and interactions of gonadotropin-releasing hormone (GnRH) analogues (lecirelin and buserelin), administration routes (intramuscular and epidural), and initial estrus cycle phases (follicular and luteal) on fertility outcomes in cyclic dairy cows subjected to the Ovsynch protocol. Results A total of 406 multiparous Holstein cows were randomly assigned to four groups: intramuscular lecirelin (Lim, n = 102), intramuscular buserelin (Bim, n = 102), epidural lecirelin (Lepi, n = 101), and epidural buserelin (Bepi, n = 101). During the Ovsynch protocol, the first GnRH treatment was administered on D0, followed by PGF2α on D7, the second GnRH treatment on D9, and fixed-time artificial insemination (FTAI) 20 h later on D10. At each GnRH administration, cows received either 62.5 µg lecirelin acetate or 10 µg buserelin acetate by the intramuscular or epidural route. Blood samples for serum progesterone (P4) determination were collected on D0, D7, D9, D10, and D13. The initial cyclic phase was determined on D0 by ovarian ultrasonography and serum P4 concentration. Pregnancy status was assessed on D30 after FTAI, and pregnancy losses on D60. No significant differences in pregnancy or pregnancy-loss rates were detected between GnRH analogues or routes of administration, irrespective of the initial cyclic phase (P > 0.05). Likewise, within each initial cyclic phase, the route of administration did not significantly affect pregnancy rate (P > 0.05), although opposite numerical trends were observed. Pregnancy rates were numerically higher after intramuscular administration in cows starting the protocol during the luteal phase (44.31% vs. 31.95%, P = 0.083), but numerically higher after epidural administration in those starting during the follicular phase (46.66% vs. 34.48%, P = 0.083). Epidural GnRH administration was also associated with higher P4 concentrations on D13 (P < 0.001). Conclusion Consequently, although changing the GnRH analogue and administration route did not significantly affect overall fertility outcomes, the findings suggest a possible phase-dependent relationship between administration route and pregnancy outcome. However, this trend requires confirmation in further studies.

Key findings

• Not reported in abstract.

Limitations

• Not reported in abstract.

Elsewhere in the Gonadorelin (GnRH) corpus