World Rabbit Science

In vivo rabbit embryo production and cryopreservation review. Application to ex situ conservation and rederivation

Jose S. Vicente, María P. Viudes-de-Castro, Francisco Marco-Jiménez — Fri, 30 Jun 2023 00:00:00 +0200

The development of reproductive technologies in this species is contributing decisively to the development of rabbit farming and the preservation of genetic resources. Obtaining embryos is an essential step to both genetic diffusion and the preservation of genetic resources from genetic erosion or natural disasters. In rabbits, it is common for embryos to be recovered post-mortem after ovarian hyperstimulation with gonadotrophins, although the quality and number of embryos are variable, affecting the embryo viability and offspring rate by the donor. In vivo embryo production within a conservation programme aims not only to obtain a large number of embryos, but also that they come from a greater number of male and female origins, in order to ensure an adequate representation of the original population. This is why both the quality and quantity of embryos obtained per donor rabbit and the rate of donors with offspring after embryo cryopreservation must be considered, as well as the response of the embryos to the chemical, physical and physiological stress to which they are subjected in the rederivation process and its postnatal repercussions on those that survive. Rederived rabbits from cryopreserved and transferred embryos showed phenotypic growth changes, which calls into question the neutrality of the technique and its usefulness in those cases in which a control population is required.

Managing sexual receptivity and ovulation induction in rabbit does: evidence from recent research

Pilar G. Rebollar, María Arias-Álvarez, Pedro L. Lorenzo, Rosa M. García-García — Fri, 30 Jun 2023 00:00:00 +0200

The sexual receptivity and ovulation induction of the reproductive rabbit are key points determining their success in productive life. Adequate synchronisation of the sexual receptivity methods of inseminated rabbit does unquestionably favours fertility and prolificacy outcomes. This review aims to bring together the different methods applied in synchronising primiparous rabbits and the consequences at metabolic, endocrine and ovarian levels, as well as in the embryonic, foetal and post-natal development that our research group has studied over the years. Likewise, the latest advances regarding ovulation induction in the rabbit are described, as well as the search for alternatives to the intramuscular injection of synthetic analogues of gonadotropins and seminal plasma components that could be involved in this process. Different experiments performed with a physiological basis confirm that nerve stimulation during artificial insemination or coitus is especially important in the ovulation induction reflex in rabbit females.

Three decades of progress in artificial insemination in rabbit farming: a review

Fri, 30 Jun 2023 00:00:00 +0200

The commercial use of artificial insemination (AI) in rabbit farming is relatively recent, especially when compared to other species such as cattle or swine, in which AI has been used for more than 60 years. The large-scale use of AI in rabbit farming dates back to the late 80s. However, despite its short journey, it has not stopped evolving. Although there have been numerous changes, in this review article we aim to highlight two important milestones in optimisation of this technique: the introduction of biostimulation and the addition of Gonadotropin-releasing hormone (GnRH) analogues to the seminal dose to induce ovulation. In the former case, by means of different methods of biostimulation, such as feed and light flushing and/or separation of the litter in the days prior to AI, the use of hormones to synchronise heat with the moment of AI was practically eliminated. Nowadays, the possibility of using pheromones with the same objective is under research, even to increase ovulation rate or improve semen production. Although there are pheromones on the market labelled for use in other species, in the case of rabbit the knowledge of them is limited. Nevertheless, given the verified effects that pheromones produce in other animals, expectations are high. In the latter case, after several attempts by using other methods, the technique commonly used to induce ovulation was the intramuscular administration of GnRH or its synthetic analogues. However, in recent years, it has been proven that administration of GnRH through the vagina is possible, added to the seminal dose, which offers numerous advantages regarding health, animal welfare and the workforce needed. Recently, the European Medicines Agency (EMA) approved this practice, so in the near future it will probably become the most widely used method. Even so, there is still room for improvement, as the dosage of GnRH needed is higher than the one administered intramuscularly. Research on this topic allows us to predict that this problem should be solved in the coming years. Other alternatives such as the β-Nerve Growth Factor need further research to become a feasible option.

Trends in rabbit insemination extenders for fresh and frozen semen. A review

María P. Viudes-de-Castro, José S. Vicente — Fri, 30 Jun 2023 00:00:00 +0200

Artificial insemination (AI) has become a popular technique in rabbit farms worldwide. This report discusses the progress made on semen extenders used in rabbit AI, setting out the latest innovations. Fresh and frozen semen have different requirements, so the extender composition will vary depending on the type of semen used. We discuss the endocrine supplementation of extenders for ovulation induction, the use of active molecules as an alternative to conventional antibiotics and the extenders developed for rabbit sperm cryopreservation.

Environmental and genetic factors affecting litter size components in rabbits

Fri, 30 Jun 2023 00:00:00 +0200

In rabbits, ovulation rate is, together with prenatal survival, one of the main limiting factors for litter size. Both components are affected by several factors related to females and their environment. Thus, understanding these components and their factors of variation is key in designing diets, optimisation of reproductive performance and genetic selection. In this review, authors summarise the main components of litter size and their environmental factors of variation. Genetic factors and the main results of genetic selection programmes on components of litter size are also summarised. In this regard, a negative effect of dietary restriction and reduced day light hours is found, as well as a positive effect of body condition, parity order and age of female on ovulation rate. However, an increase in deterioration of oocyte quality has been reported as ovulation rate increases, leading to decreased embryonic and foetal survival. Dietary restriction and heat stress also have a negative effect on embryonic and foetal survival, increasing the failures during gestation while good vascularisation and enough available space in uterine horn are keys to embryonic and foetal survival. Ovulation rate was proposed as indirect selection criterion to improve litter size due to higher heritability. However, this selection was relevant, but it did not modify litter size because of an increase in prenatal mortality. Uterine capacity has been directly related to prenatal survival, although its selection has also been unsuccessful in increasing litter size.

Effect of an extender enriched with algerian date palm pollen on chilled semen characteristics of rabbit bucks at different ages

Fri, 30 Jun 2023 00:00:00 +0200

In the present study, we evaluated the effect of various concentrations of date palm pollen (DPP) aqueous extract on rabbit sperm during storage at 4°C for 48 h. Semen was collected from old and young rabbit bucks using an artificial vagina and initially evaluated for sperm quality. The sperm were diluted in Tris buffer supplemented with (20, 40, 80 mg/mL) of DPP aqueous extract. The extended samples were stored at 4°C for 48 h. Sperm motility and motion kinetics were assessed after 2, 4, 24 and 48 h of storage. At each time, an aliquot was frozen for the analytical evaluation of thiobarbituric acid reactive substances (TBARS) (lipid peroxidation) and tocols (vitamin E). Proximate composition, antioxidant and sugar content were evaluated in DPP. The results showed that DPP was characterised by a high proportion of protein (27.10%) and ash (18.43%), whereas the lipid fraction was very low (0.51%) and total sugar was also high (16.25 g/100 g of fresh matter, f.m.). Regarding the antioxidants content, the sum of tocols showed a total value of 26.48 mg/g f.m. The total polyphenols content was 5.01 mg gallic acid equivalents/g f.m, and polyunsaturated fatty acids was around 30%. Date palm pollen extract had a dose-dependent effect on sperm parameters (curvilinear velocity [VCL] mainly) of old rabbit, although a null or negative effect was recorded at doses >DPP40. Conversely, in optimal conditions (i.e. young rabbit semen), the addition of pollen had no effect on sperm traits (motility and VCL). The progressive increase in DPP, despite providing sperm with an additional amount of tocols, also caused higher tocol consumption and an increase in lipid oxidation. In particular, DPP80 increased the TBARS level in sperm of both rabbit ages. The better trend was found in DPP20, where the tocol consumption figures were 10.46 % and 15.28 %, respectively, in old and young bucks, and the lipid oxidation was lower compared to the higher doses of DPP. In conclusion, the findings of this study demonstrated that supplementation of DPP extract to Tris buffer extender enhanced chilled rabbit semen traits only if administered in old rabbit semen at concentration lower than 40 mg/mL.