Reproductive Performance of Female Rabbits Inseminated with Extenders Supplemented with GnRH Analogue Entrapped in Chitosan-Based Nanoparticles

SIMPLE SUMMARY: Ovulation in female rabbits is induced via the sensory stimulation associated with mating. Consequently, when artificial insemination is used, as there is no stimulation via coitus, an analogue of the hormone responsible for ovulation induction must be used, which could be performed intramuscularly, intravenously, or intravaginally. Addition of the hormonal analogue to the seminal dose, for intravaginal administration, is the least stressful way to induce ovulation in does. However, due to the high level of enzymes present in rabbit seminal plasma and the poor permeability of the vaginal mucosa, the amount of analogue required for successful ovulation induction via the vaginal route may be 20–30 times the dose needed for the intramuscular route. Protection of the analogue via nanoencapsulation can help overcome enzyme degradation and improve its bioavailability. The efficacy of two extenders with chitosan–dextran sulphate or chitosan–alginate nanoparticles entrapping the hormone analogue will be studied. The main aim of the current work is to assess the effect of both encapsulation systems on reproductive performance after insemination. Results showed that both nanoencapsulation systems used here are an efficient way of intravaginal ovulation induction, allowing a reduction in the concentration of the hormone used in artificial insemination to four micrograms per female without affecting fertility and prolificacy. ABSTRACT: Rabbit is a reflexively ovulating species. Accordingly, in the practice of artificial insemination (AI) ovulation must be induced via exogenous GnRH (Gonadotropin-Releasing Hormone) administration, which may be performed intramuscularly, subcutaneously, or intravaginally. Unfortunately, the bioavailability of the GnRH analogue when added to the extender is lower due to the proteolytic activity in the seminal plasma and the poor permeability of the vaginal mucosa. The aim of the study was to refine the practice of AI practice in rabbits by replacing parenteral GnRH analogue administration (subcutaneous, intravenous, or intramuscular injection) with intravaginal application, while reducing its concentration in the diluent. Extenders containing the buserelin acetate in chitosan–dextran sulphate and chitosan–alginate nanoparticles were designed and 356 females were inseminated. Reproductive performance of females inseminated with the two experimental extenders, receiving 4 μg of buserelin acetate intravaginally per doe, was compared with that in the control group, the does of which were inseminated with the extender without the GnRH analogue and induced to ovulate with 1 μg of buserelin acetate administered intramuscularly. The entrapment efficiency of the chitosan–dextran sulphate complex was higher than that of chitosan–alginate. However, females inseminated with both systems showed similar reproductive performance. We conclude that both nanoencapsulation systems are an efficient way of intravaginal ovulation induction, allowing a reduction in the level of the GnRH analogue normally used in seminal doses from 15–25 μg to 4 μg.