Sperm sex-sorting and preservation for managing the sex ratio and genetic diversity of the southern white rhinoceros (Ceratotherium simum simum)

Sperm Cooling as an Assisted Reproduction Tool for Wildlife: An Underrated Technology

The search for assisted reproduction techniques applied to the conservation and even the genetic improvement of wild species is becoming increasingly common. Regarding conservation of male gametes from wild animals, although current advances are focused on cryopreservation, the development of protocols for sperm refrigeration seems to be underrated, despite its various advantages and applications. Therefore, this review aims to highlight the importance of short-term conservation of sperm from wild mammals, report the development of state-of-the-art refrigeration protocols for both ejaculated and epididymal sperm, and evaluate the challenges and prospects of their application.

Increasing the Yield and Cryosurvival of Spermatozoa from Rhinoceros Ejaculates Using the Enzyme Papain

Simple Summary

Efficient collection and cryosurvival of semen from threatened wildlife species is key for the success of artificial reproductive technologies (ARTs). The viscous nature of ejaculates often collected from species such as rhinoceros, elephant, hippopotamus and primate, render the majority of spermatozoa collected useless and is therefore wasted. The enzyme papain has been used to reduce the viscosity of camelid semen but has yet to be tested in wildlife species. Therefore, the current study investigated the ability of papain to improve the yield and quality of spermatozoa collected from viscous fractions of the rhinoceros ejaculate during cryopreservation. Papain increased the quantity of useable spermatozoa collected from ejaculates, as well as the motility prior to freezing. It also improved the post-thaw motility, velocity, linearity and straightness of samples compared to spermatozoa frozen from the sperm-rich fraction of the ejaculate. There was no detrimental effect on membrane characteristics or DNA integrity. These results show that treating rhinoceros ejaculates with papain is able to salvage valuable spermatozoa and improve survival post-thaw, ultimately increasing the success of ARTs and creation of biobanks for the maintenance and survival of threatened species.

Abstract

The preservation of rhinoceros semen is vital for captive breeding programs. While successful collection and cryopreservation of rhinoceros semen has been reported, the volume and quality of semen produced is often low due to the high viscosity associated with ejaculates collected via electroejaculation. Reducing semen viscosity would enable access to previously unusable spermatozoa from viscous fractions and could improve quality post-thaw. The enzyme papain successfully reduced the viscosity of camelid semen but has yet to be tested in wildlife species. This study assessed the influence of papain on the in vitro quality of rhinoceros spermatozoa during cryopreservation using advanced semen assessment. In experiment 1, the motility of spermatozoa from the viscous fraction of an ejaculate, either untreated or treated with papain and its inhibitor E-64 prior to cryopreservation, was assessed post-thaw. In experiment 2, spermatozoa from papain-treated viscous fractions were compared to spermatozoa frozen from untreated sperm-rich fractions pre-freeze, as well as after 0, 1.5 and 3 h of incubation post-thaw (37 °C). Papain significantly increased the quantity of spermatozoa collected from ejaculates, as well as the motility prior to freezing. Papain also improved the post-thaw motility, velocity, linearity and straightness of samples compared to sperm-rich samples, with no detriment to sperm viability, lipid membrane disorder, production of ROS or DNA integrity (p < 0.05). Results show the benefit of supplementing rhinoceros spermatozoa with papain prior to cryopreservation on sperm cryosurvival and demonstrates the potential of using papain to improve the success of cryopreservation protocols, not only for the rhinoceros, but also for other wildlife species.

Game-Changing Approaches in Sperm Sex-Sorting: Microfluidics and Nanotechnology

Simple Summary

Sexing of sperm cells, including the capacity to preselect the sex of offspring prior to reproduction, has been a major target of reproductive biotechnology for a very long time. The advances in molecular biology, biophysics, and computer science over the past few decades, as well as the groundbreaking new methods introduced by scientists, have contributed to some major breakthroughs in a variety of branches of medicine. In particular, assisted reproduction is one of the areas in which emerging technologies such as nanotechnology and microfluidics may enhance the fertility potential of samples of sex-sorted semen, thus improving the reproductive management of farm animals and conservation programs. In human medicine, embryo sex-selection using in vitro fertilization (IVF) and preimplantation genetic testing (PGT) is accepted only for medical reasons. Using sex-sorting before IVF would enable specialists to prevent sex-linked genetic diseases and prevent the discharge of embryos which are not suitable for transfer due to their sex.

Abstract

The utilization of sex-sorted sperm for artificial insemination and in-vitro fertilization is considered a valuable tool for improving production efficiency and optimizing reproductive management in farm animals, subsequently ensuring sufficient food resource for the growing human population. Despite the fact that sperm sex-sorting is one of the most intense studied technologies and notable progress have been made in the past three decades to optimize it, the conception rates when using sex-sorted semen are still under expectations. Assisted reproduction programs may benefit from the use of emergent nano and microfluidic-based technologies. This article addresses the currently used methods for sperm sex-sorting, as well as the emerging ones, based on nanotechnology and microfluidics emphasizing on their practical and economic applicability.

Managed wildlife breeding-an undervalued conservation tool?

Knowledge of and the technologies and resources applied to the ex situ care for wildlife have improved greatly in recent years. This has resulted in numerous successes bringing back populations from the brink of extinction by the reintroduction or restoration of animals from conservation breeding programmes. Controlled breeding of wildlife by humans is discussed controversially in society and in scientific circles and it faces a number of significant challenges. When natural breeding fails, Assisted Reproduction Technologies (ART) have been postulated to increase reproductive output and maintain genetic diversity. Furthermore, technical advances have improved the potential for successful collection and cryopreservation of gametes and embryos in many wildlife species. With the aim of creating a better understanding of why ex situ and in situ conservation of threatened species must complement each other, and under which circumstances ART provide additional tools in the rescue of a threatened population, we elucidate the current situation here by using as examples three different megavertebrate families: elephantidae, rhinoceridae and giraffidae. These mammal families consist of charismatic species, and most of their members are currently facing dramatic declines in population numbers. On the basis of these and other examples, we highlight the importance of captive zoo and other managed wildlife populations for species survival in a human dominated world. Without the possibility to study reproductive physiology in trained or habituated captive individuals, major advances made in wildlife ART during the past 20 years would not have been possible. This paper reviews the benefits and future challenges of large mammal conservation breeding and examines the role of assisted reproduction in such efforts.

Animal protein-free OptiXcell and shortened equilibration periods can replace egg yolk-based extender and slow cooling for rhinoceros semen cryopreservation

OptiXcell (OP) was tested as an animal protein-free alternative to an egg yolk-based extender for rhinoceros semen cryopreservation and shorter chilling/equilibration periods were evaluated. Semen was collected from three rhinoceros species: black (Diceros bicornis; n = 2), white (Ceratotherium simum; n = 2), and greater one-horned (GOH; Rhinoceros unicornis; n = 3). Controls were diluted with equine extender (EQ) or OP and equilibrated for 1 h. Treatments were diluted with extender and cooled for 15 min (fast: FEQ; FOP) or not cooled (immediate: IEQ; IOP), prior to cryopreservation. Motility decreased post-thaw (EQ: 50.7 ± 5.2%; OP: 52.9 ± 3.4%) from fresh (82.9 ± 2.9%), was higher in OP than IOP (38.6 ± 4.9%; P ≤ 0.05) and decreased over time (P ≤ 0.05). Post-thaw acrosomal integrity was lower in EQ, FEQ, and IEQ (56.9 ± 0.7; 56.6 ± 4.5; 54.9 ± 2.9%) than OP, FOP, IOP (71.8 ± 4.7; 71.9 ± 3.8; 69.9 ± 4.5%) and fresh (72.6 ± 1.4%; P ≤ 0.05). Progression and viability were lower in EQ (2.8 ± 0.2; 61.9 ± 7.4%) and OP (3.1 ± 0.2; 53.4 ± 6.9%) than fresh (3.7 ± 0.2; 87.2 ± 1.3%), decreased over time (P ≤ 0.05) but not different among treatments (P > 0.05). Morphology did not differ between fresh (75.0 ± 4.9% normal) and any treatment group (70.0-77.8%) or over time (P > 0.05). OptiXcell is comparable to egg yolk-based EQ when used for rhinoceros semen cryopreservation. Furthermore, chilling/equilibration can be reduced with little impact on sperm characteristics.

Comparison of soy lecithin, coconut water, and coconut milk as substitutes for egg-yolk in semen cryodiluent for black rhinoceros (Diceros bicornis) and Indian rhinoceros (Rhinoceros unicornis)

Semen cryopreservation for the black rhinoceros (Diceros bicornis) and Indian rhinoceros (Rhinoceros unicornis) relies on extenders containing egg-yolk (EY). Use of such media is not ideal as inter-batch composition varies and there is risk of pathogenic contamination. The goal of this study was to test animal protein-free extenders. Semen collected via electroejaculation from 10 rhinoceros (6 black, 4 Indian) was diluted with extender containing EY, 1% or 2% soy lecithin (1%SL; 2%SL), coconut water (CW), or coconut milk (CM), cryopreserved and evaluated for sperm motility, viability, morphology, progression, and acrosomal integrity at 0, 1, 3, 6 and 24 h post-thaw. Mean ± SD fresh ejaculate motility was 84.5 ± 7.6%, progression: 3.6 ± 0.6 (scale 0-5), viability: 83.4 ± 7.1%, intact acrosomes: 71.3 ± 6.9%, and morphologically normal: 78.8 ± 13.6%. Motility and progression decreased in all groups post-thaw, were greatest in EY, and decreased over time (P ≤ 0.05). Motility and progression did not differ (P > 0.05) between 1%SL and 2%SL, but were lower (P ≤ 0.05) in CM and CW, and acrosomal integrity was higher (P ≤ 0.05) in EY, 1%SL and 2%SL than in CM and CW. Post-thaw viability was greatest in EY and 2%SL followed by 1%SL, then CM and CW (P ≤ 0.05). Morphology did not differ among treatments (P > 0.05). Morphology, acrosomal integrity, and viability were maintained over time (P > 0.05). Although some rhinoceros sperm survived cryopreservation in SL treatments, reduced post-thaw motility rendered all treatments inadequate substitutes for EY-based extenders.

Early fetal sexing in the rhinoceros by detection of male-specific genes in maternal serum

Genetic sexing of animals with long gestation time benefits the management of captive populations. Here, X and Y chromosome-specific primers, based on equine gene sequencing data, were developed and tested on captive rhinoceroses (10 males, 20 females) representing four species (Diceros bicornis, Certaotherium simum simum, Rhinoceros unicornis, and Dicerorhinus sumatrensis). The Y chromosome-specific primer set targeted SRY (Sex-determining region Y), and amplified a 177-bp product following PCR of DNA extracted from males, but not females, of all species. A primer set based on the equine AMEL (Amelogenin) gene resulted in a 232-bp product following PCR of all rhinoceros species. These gene-specific primer sets were then evaluated for their ability to determine gender in cell-free DNA from rhinoceros serum. Modifications to the original extraction and PCR protocols were required to obtain sufficient DNA quantities from serum, and both DNA yield and PCR amplification were substantially reduced or absent following multiple freeze-thaw cycles of serum. When fresh serum from 14 pregnant rhinoceroses (ultimately bearing seven male and seven female calves), representing four species at different stages of gestation (Days 61-490), were probed in a PCR-based assay, an accuracy of 71% was achieved for male-specific gene detection of SRY, which improved to 100% by including a reamplification step into the protocol. Such early sex determination should be a valuable tool for current management practices as well as future assisted reproduction of rhinoceroses.