Intravaginal GnRH analogues in rabbits: Fertirelin as the most effective option for ovulation induction

Rabbits are reflex ovulators that require exogenous hormonal stimulation, typically a Gonadotropin-releasing hormone (GnRH) analogue, to induce ovulation during Artificial Insemination (AI). While intramuscular injection is the reference standard, intravaginal administration via semen supplementation offers welfare advantages by reducing handling. However, this route often requires higher doses due to rapid proteolytic degradation. This study evaluated three GnRH analogues (fertirelin, buserelin, and deslorelin) administered intravaginally in New Zealand White rabbits, assessing on ovulation induction, reproductive performance, and the minimum effective concentration. Three experiments were performed, including direct ovulation assessment by laparoscopy and evaluation of delivery rate and prolificacy in lactating and non-lactating does. The semen extender included 20 mM EDTA to enhance hormone stability. Ovulation frequency and delivery rate were significantly affected by the analogue used (p < 0.05). Fertirelin consistently showed the highest efficacy, achieving ovulation and delivery rates equivalent to the intramuscular control, even at a reduced dose of 1 μg. Deslorelin showed intermediate efficacy, whereas intravaginal buserelin yielded the lowest results. Non-lactating does showed higher delivery rates than lactating ones (P < 0.05), however, no significant interaction was detected between analogue type and physiological status, indicating consistent fertirelin efficacy across reproductive conditions. Although no-significant (p = 0.086), a biological trend suggested that the relative advantage of fertirelin may become pronounced under demanding physiological conditions such as lactation. Neither analogue nor physiological status influenced total or live litter size. The stable performance of fertirelin irrespective of physiological condition supports its superior receptor affinity, making it a promising candidate for welfare-oriented intravaginal AI protocols in rabbits.