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Rabbit is an induced ovulatory species, so ovulation takes place after mating. Traditionally, exogenous and synthetic hormonal factors (administered by intramuscular and intravaginal route) such as GnRH and analogues, or different physical procedures (i.e. stimulation by intravaginal cannula) have been used to induce ovulation in females when artificial insemination is applied in rabbit farms. Restriction and public rejection of the use of hormones is leading to the study of the seminal plasma components with potential action on ovulation induction. The aim of the present review is to collect and summarise the strategies used in recent years to trigger ovulation and improve rabbit fertility management with respect to more animal-friendly manipulation methods. Furthermore, special attention has been paid to the use of a semen component (as endogen molecule) such as beta nerve growth factor (β-NGF) in male and female rabbit reproductive physiology. This neurotrophin and its receptors (TrKA and p75NTR) are abundantly distributed in both male and female rabbit reproductive tracts, and it seems to have an important physiological role in sperm maturation and behaviour (velocity, apoptosis and capacitation), as well as a modulatory factor of ovulation. Endogen β-NGF is diluted in the seminal doses with the extenders; hence it could be considered an innovative and alternative strategy to avoid the current exogenous (by intramuscular route) and stressful hormonal treatments used in ovulation induction. Their addition in seminal dose could be more physiological and improve animal welfare in rabbit farms.

The neurotrophin β-nerve growth factor (NGF) has been described as an important mediator of seminal plasma-induced ovulation in reflexive ovulators like camelids, but this action has not been evidenced in rabbits. In this study, the mRNA expression of NGF was analysed in rabbit male organs by PCR and in a purified basic fraction of seminal plasma by liquid chromatography mass spectrometry. Besides, the ovulatory response [ovulation rate (OR), corpora lutea number, LH peak and progesterone profile] of 27 rabbit does was recorded after injection with murine NGF, gonadoreline (GnRH) or saline solution (SS). An empty catheter was introduced through the vagina (n = 4 animals per group) to simulate the nervous/mechanical stimulus of coitus. Molecular studies confirmed the expression of β-NGF mRNA in the prostate, seminal gland and testicles of male adult rabbits, and the presence of the protein in seminal plasma. For the in vivo experiment, all GnRH-group does exhibited a significantly higher OR (100%) compared to females treated with NGF (30%) and SS (25%), who showed significantly lower LH and progesterone concentrations at 120 min. However, in the non-vaginally stimulated animals, only the gonadoreline group ovulated properly, since no ovulation was recorded in the SS group, and only 17% of the NGF does ovulated; this was associated to a tendency to a higher rate of anovulatory haemorrhagic follicles. mRNA expression of NGF and its presence in seminal plasma evidence a role in rabbit reproduction. Nevertheless, murine NGF triggered some stimulatory effect in the females but not enough to elicit a significant ovulatory response.

The neurotrophin β-nerve growth factor (NGF) has been described as an important mediator of seminal plasma-induced ovulation in reflexive ovulators like camelids, but this action has not been evidenced in rabbits. In this study, the mRNA expression of NGF was analysed in rabbit male organs by PCR and in a purified basic fraction of seminal plasma by liquid chromatography mass spectrometry. Besides, the ovulatory response [ovulation rate (OR), corpora lutea number, LH peak and progesterone profile] of 27 rabbit does was recorded after injection with murine NGF, gonadoreline (GnRH) or saline solution (SS). An empty catheter was introduced through the vagina (n=4 animals per group) to simulate the nervous/mechanical stimulus of coitus. Molecular studies confirmed the expression of β-NGF mRNA in the prostate, seminal gland and testicles of male adult rabbits, and the presence of the protein in seminal plasma. For the in vivo experiment, all GnRH-group does exhibited a significantly higher OR (100%) compared to females treated with NGF (30%) and SS (25%), who showed significantly lower LH and progesterone concentrations at 120 min. However, in the non-vaginally stimulated animals, only the gonadoreline group ovulated properly, since no ovulation was recorded in the SS group, and only 17% of the NGF does ovulated; this was associated to a tendency to a higher rate of anovulatory haemorrhagic follicles. mRNA expression of NGF and its presence in seminal plasma evidence a role in rabbit reproduction. Nevertheless, murine NGF triggered some stimulatory effect in the females but not enough to elicit a significant ovulatory response. [ABSTRACT FROM AUTHOR]