Detrimental effect on availability of buserelin acetate administered in seminal doses in rabbits

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

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.

Effect of addition of buserelin acetate to the extender on motility and viability of bovine spermatozoa

The present study was aimed to determine the effect of GnRH analog (buserelin acetate) on the quality of bovine spermatozoa stored at 16° C for 24 h. Semen collected in the summer season from June to September from healthy Polish Holstein-Friesian bulls. Ejaculates were centrifuged, divided and diluted to the final concentration of 240 × 10⁶ spermatozoa/mL using animal protein-free commercial BIOXcell^® extender (IMV Technologies, L'aigle, France) (Control) or with BIOXcell^® extender supplemented with buserelin acetate and stored 0, 8 and 24 h. Sperm motility parameters analysis was performed using a computer-assisted sperm analysis (CASA) system. The viability of spermatozoa was performed using flow cytometer. The addition of buserelin acetate to BIOXcell^® extender did positively affect the total motility (was higher in the observed samples with the addition of 2 µg/mL and 4 µg/mL than in the control group), progressive motile (forward progressing sperm was significantly increased (p < 0.05) over the control group at the 0 h and 8 h of incubation following the supplementation of 2, 4 and 8 μg/mL buserelin acetate) and viability of spermatozoa (the number of live spermatozoa was significantly higher (p < 0.05) in 2 µg/mL and 4 µg/mL samples with buserelin acetate at 8th hour of incubation and in sample with 4 µg/mL at 24th hour of incubation compared to the control group). We recommend adding 4 µg/mL to the extender to improve the quality of bovine semen.

Effects of an intravaginal GnRH analogue administration on rabbit reproductive parameters and welfare

On commercial farms, rabbit does are subjected to a reproductive rhythm that does not account for their welfare or physiology, leading to reduced longevity and consequently high annual replacement. The European Food Safety Authority (EFSA) recommends limited and infrequent use of hormone treatments, and suggests replacement with alternative methods that do not threaten animal welfare when possible. In the present study, we aimed to determine whether the GnRH analogue lecirelin acetate could be administered by inclusion in the seminal dose during insemination. Twenty 9-month-old does (Grigio del Monferrato, autochthonous Italian breed),each having two previous deliveries, were individually housed and divided into two groups at artificial insemination. The control group received 0.2 mL of intramuscular lecirelin (Dalmarelin, Fatro^®, Italy) prior to insemination. The intravaginal group was inseminated with a seminal dose that included 0.3 mL Dalmarelin. The experiment was performed for six consecutive reproductive cycles at 42-day intervals, and included a total of 120 inseminations. Prior to each insemination, the heterospermic pooled semen samples were assessed for sperm motility and morphology. Each ejaculate was divided into two samples, with and without lecirelin addition. Compared to the control group, the does with intravaginal Dalmarelin administration showed equal or greater sexual receptivity, which resulted in a higher fertility rate over increasing cycles. The seminal dose volume was very low, possibly explaining the better results in the intravaginal group, which received a similar amount of hormone (0.3 mL/doe) as the control group (0.2 mL/doe). The negative performance of the control group may have also been due to anti-GnRH formation, and the more stressful method of ovulation induction. The number of live-born kits did not significantly differ between groups. Progressive motility was significantly positively correlated with motility characteristics, including VAP, VSL, ALH, BCF, STR, and LIN. Overall, our present findings supported that the incorporation of GnRH in a seminal dose could be used for ovulation induction in rabbit does. Further studies should identify the optimal dose of GnRH for intravaginal administration, taking into account that the intravaginal absorption capacity is about 10 times smaller than the intramuscular absorption capacity.

Motility, mitochondrial membrane potential and ATP content of rabbit spermatozoa stored in extender supplemented with GnRH analogue [des-Gly10, D-Ala6]-LH-RH ethylamide

The present study was aimed to determine the effect of GnRH analogue [des-Gly10, D-Ala6]-LH-RH ethylamide on the quality of rabbit spermatozoa stored at 17°C for 3 days. Semen from 5 bucks (13 ejaculates) was used in the experiment. Ejaculates were divided and diluted at a 1:10 ratio with rabbit semen extender Galap (IMV, France) (Control) or with Galap extender supplemented with GnRH analogue [des-Gly10, D-Ala6]-LH-RH ethylamide (50 μg/ml) and stored for 3 days. Sperm motility parameters, mitochondrial membrane potential (MMP) and ATP content were as- sessed on each day of the experiment. Motility analysis was performed using a computer-assisted sperm analysis (CASA) system. The following sperm motility parameters were recorded: total motile spermatozoa, progressively motile spermatozoa, curvilinear velocity, straight-line velocity, average path velocity, linearity, straightness and amplitude of lateral head displacement. MMP was evaluated using JC-1 fluorescent dye. ATP content was assessed using a bioluminescence method. The addition of GnRH analogue [des-Gly10, D-Ala6]-LH-RH ethylamide to Galap extender did not affect any of the quality parameters studied. However, in both groups (Control and GnRH), significant changes in motility parameters (except straight-line velocity) and proportion of spermatozoa showing high MMP and ATP content were observed throughout 3 days of storage.

Induction of ovulation in rabbits by adding Lecirelin to the seminal dose: in vitro and in vivo effects of different excipients

This study evaluates the effect of Lecirelin (Dalmarelin(®), Fatro, Italy) diluted in different excipients (benzilic alcohol, benzoic acid and paraben) added to a seminal dose on LH concentrations, progesterone concentrations and ovarian status in rabbits. The in vitro effect on spermatozoa was also tested. A total of 100 multiparous female rabbits were divided into 5 groups, which at the moment of AI, received 0.2 mL (5 μg/dose) intramuscular (im) inoculation of Lecirelin (control) or the same Lecirelin dose administered intravaginally (iv) with the seminal dose alone (Lecirelin group) or with benzilic alcohol (Lecirelin BA group), benzoic acid (Lecirelin BAc group) or parabens (Lecirelin PA group) as an excipient. After 7 days, 10 rabbits per group were euthanized to analyze their ovarian status. In the control group, a high LH peak was detected 30 min post AI, while in the iv groups a slight increase in LH occurred after 120 min. The ovulation and fertility rate was similar in control and Lecirelin groups, while the lowest fertility rate was detected in the Lecirelin BA group. In a second experiment, the semen samples collected from male rabbits were diluted in TALP (control) or mixed with the 5 μg of Lecirelin solutions used in the first experiment. The highest percentage of capacitated sperm (68.3%) was recorded in the Lecirelin PA. The lowest percentages were observed in the Lecirelin BA and BAc groups. In conclusion, the iv administration of Lecirelin represents an alternative method for simplifying rabbit insemination procedures.

Live birth from slow-frozen rabbit oocytes after in vivo fertilisation

In vivo fertilisation techniques such as intraoviductal oocyte transfer have been considered as alternatives to bypass the inadequacy of conventional in vitro fertilisation in rabbit. There is only one study in the literature, published in 1989, that reports live offspring from cryopreserved rabbit oocytes. The aim of the present study was to establish the in vivo fertilisation procedure to generate live offspring with frozen oocytes. First, the effect of two recipient models (i) ovariectomised or (ii) oviduct ligated immediately after transfer on the ability of fresh oocytes to fertilise were compared. Second, generation of live offspring from slow-frozen oocytes was carried out using the ligated oviduct recipient model. Throughout the experiment, recipients were artificially inseminated 9 hours prior to oocyte transfer. In the first experiment, two days after unilateral transfer of fresh oocytes, oviducts and uterine horns were flushed to assess embryo recovery rates. The embryo recovery rates were low compared to control in both ovariectomised and ligated oviduct groups. However, ligated oviduct recipient showed significantly (P<0.05) higher embryo recovery rates compared to ovariectomised and control-transferred. In the second experiment, using bilateral oviduct ligation model, all females that received slow-frozen oocytes became pregnant and delivered a total of 4 live young naturally. Thus, in vivo fertilisation is an effective technique to generate live offspring using slow-frozen oocytes in rabbits.