In vitro-production of embryos using immature oocytes collected transvaginally from superstimulated wood bison (Bison bison athabascae)

Review: Reproductive physiology of bison and application of assisted reproductive technologies to their conservation

Bison are an ecologically and culturally important species on the European and North American continents. Their near extirpation was met with conservation efforts that prevented their extinction but left few animals or highly fragmented populations. Contemporary conservation efforts are focused on building ecologically and genetically sustainable bison herds for long-term conservation of the species. Assisted reproductive technologies (ARTs) can play a key role in building these herds by facilitating the movement of genetics in the form of gametes and embryos, while protecting animal well-being and ensuring biosecurity of existing bison herds. In addition, ARTs such as gamete and embryo cryopreservation can be used to protect against future losses of genetic diversity through biobanking. In this review, a brief summary of basic bison reproductive physiology is presented followed by an overview of the current state of ART in Bison bison (American bison) and Bison bonasus (European bison or wisent). Research on ART ranging from artificial insemination to in vitro embryo transfer and cloning is discussed with particular regard to the application of ART for conservation purposes. While significant progress has been made in ART for bison, there are still many opportunities to improve these technologies and expand their impact for bison conservation.

Strategies for oocyte collection and in vitro embryo production in free-roaming bison herds

The study was conducted to test the feasibility of protocols for field collection of cumulus-oocyte complexes (COC) for in vitro embryo production (IVP) in wild bison. The study was done with captive wood bison during the anovulatory season. In Experiment 1, the efficiency of transvaginal ultrasound-guided COC collection was compared between bison restrained in a squeeze chute without sedation vs in lateral recumbency after chemical immobilization using a dart gun (n = 8/group). In Experiment 2, a 2 × 2 design was used to examine the effects of superstimulation treatment [single dose of equine chorionic gonodotrophin (eCG) vs multiple doses of follicle stimulating hormone (FSH)] and method of drug administration (manual injection vs field darting) on COC collection and IVP. In Experiment 1, no difference was detected between chute-restrained vs chemically immobilized groups in the time required to complete COC collections, the number of follicles aspirated (11.5 ± 1.9 vs 9.3 ± 1.8; P = 0.4) or the COC recovery rate [COC recovered/follicle aspirated; 58/92 (63%) vs 44/69 (64%); P = 0.9]. In Experiment 2, no differences were detected between superstimulation treatments (eCG vs FSH). The total number of follicles available for aspiration did not differ between manual injection and field darting (23.9 ± 2.7 vs 21.6 ± 1.9; P = 0.4). Compared with the random start unstimulated group, the embryo production rate was higher [18/132 (14%) vs 53/189 (28%); P = 0.04] after wave synchronization and superstimulation. Results suggest that COC collection is equally feasible in a recumbent position after chemical immobilization as those bison restrained in a standing position in a hydraulic chute. Ovarian superstimulation with a single-dose eCG protocol is as effective as a multiple-dose FSH protocol, and field darting is as effective as chute-side administration of superstimulation treatments. The strategies in the present study are ready to be incorporated into field collections in free-roaming bison herds.

Embryo production by in vitro fertilization in wild ungulates: progress and perspectives

Wild ungulates are of fundamental importance for balancing ecosystems, as well as being the species of economic interest. Increasing concern over the accelerated population reduction of these species has resulted in the development of assisted reproduction techniques, such as in vitro fertilization (IVF), as a tool for conservation and multiplication. In the present scenario, IVF protocols were developed based on the methodologies used for domestic ungulates. Nevertheless, owing to the physiological and reproductive differences among the species, several factors associated with IVF and its relationship with the characteristics of the species of interest require clarification. In vitro conditions for the collection and selection of female and male gametes, oocyte maturation, sperm capacitation, co-incubation of gametes, and embryonic development can influence IVF results. Therefore, the present review considers the main advances in the methodologies already used for wild ungulates, emphasizing the strategies for improving the protocols to obtain better efficiency rates. Additionally, we discuss the conditions of each IVF stage, with emphasis on aspects related to in vitro manipulation and comparability with the protocols for domestic ungulates.

Effect of season and superstimulatory treatment on in vivo and in vitro embryo production in wood bison (Bison bison athabascae)

Two experiments were done using a two-by-two design to determine the effects of season and superstimulatory protocol on embryo production in wood bison. In Experiment 1 (in vivo-derived embryos), ovarian superstimulation was induced in female bison during the ovulatory and anovulatory seasons with either two or three doses of FSH given every-other-day (FSH × 2 vs. FSH × 3, respectively). Bison were given hCG to induce ovulation, inseminated 12 and 24 hr after hCG, and embryos were collected 8 days after hCG (n = 10 bison/group). In Experiment 2 (in vitro embryo production), ovarian superstimulation was induced in female bison during the ovulatory and anovulatory seasons with two doses of FSH, and in vivo maturation of the cumulus-oocyte complexes (COC) was induced with hCG at either 48 or 72 hr after the last dose of FSH. COC were collected 34 hr after hCG, and expanded COC were used for in vitro fertilization and culture. In Experiment 1, the number of follicles ≥9 mm, the proportion of follicles that ovulated, the number of CL, and the total number of ova/embryos collected did not differ between seasons or treatment groups, but the number of transferable embryos was greater (p < .05) in the ovulatory season. In Experiment 2, no differences were detected between seasons or treatment groups for any end point. The number of transferable embryos produced per bison was greatest (p < .05) using in vitro fertilization and was unaffected by season (1.5 ± 0.2 and 1.1 ± 0.3 during anovulatory and ovulatory seasons, respectively), in contrast to in vivo embryo production which was affected by season (0.1 ± 0.01 and 0.7 ± 0.2 during anovulatory and ovulatory seasons, respectively). Results demonstrate that transferable embryos can be produced throughout the year in wood bison by both in vivo and in vitro techniques, but the efficiency of embryo production of in vivo-derived embryos is significantly lower during the anovulatory season.

In Vitro Production of Bison Embryos

Bison are an iconic species of cultural, conservation, and commercial interest. Various assisted reproductive technologies have been tested in bison over the last few decades (e.g., superovulation and embryo transfer), but their efficiencies are low. Since 2007, several methods for producing bison embryos in vitro have been published. All of these methods are based on cattle embryo production models and have varying degrees of success with regard to embryo production rates. In this chapter, a brief summary of these reports is presented followed by a detailed protocol that has been successfully used to produce bison embryos in vitro and live offspring following embryo transfer.

Obtaining Wisent early blastocyst in vitro is a basic for protection and creation of biodiversity for this threatened species

Wisent, or European bison (Bison bonasus), is listed as "vulnerable" on the IUCN Red List of Threatened Species and is therefore protected by international law. For the first time, a Wisent embryo has been obtained in vitro. This procedure creates a new opportunity to protect and increase Wisent reproductive potential and thereby opens new possibilities for the establishment of a controlled and broad reserve of the gene pool.