Sperm and testicular measurements and sperm cryopreservation in the giraffe (Giraffa)

Cryopreservation of Giraffe Epidydimal Spermatozoa Using Different Extenders and Cryoprotectants

Simple Summary

Giraffe numbers have been plummeting over the last 30 years by 30–40%. As such, efforts to manage in situ and ex situ populations are increasing. Assisted reproduction techniques such as sperm cryopreservation can help preserve the genetic diversity of giraffe subspecies or enhance genetic exchange between populations. However, to date, the post-thaw motility of recovered sperm has been variable. In this study, spermatozoa were collected from the epididymides of seven giraffes to investigate whether an alternative cryoprotectant could improve sperm motility following conventional cryopreservation. For this, we compared the motility and viability of sperm prior to and after freezing in three different extenders: a commercial equine extender (BotuCrio^®; Nidacon, Moedal, Schweden), a commercial bovine extender (Steridyl, Minitube, Tiefenbach, Germany), and an in-house “made” bovine egg yolk extender (TEY). Each was further supplemented with either glycerol or a mix of glycerol and methylformamide cryoprotectants. The results show that spermatozoa frozen with a mix of two cryoprotectants had significantly higher post-thaw motility compared to glycerol alone. Specifically, spermatozoa frozen in TEY and a mix of cryoprotectants achieved post-thaw sperm motility of 57 ± 3%. These results might serve as a blueprint for an improved protocol for giraffe sperm cryopreservation.

Abstract

Giraffe numbers have plummeted over the last 30 years by 30–40%. Thus, their conservation status has been raised from least concern to vulnerable. Efforts to manage in situ and ex situ populations are increasing. Assisted reproduction techniques (ART) such as sperm cryopreservation could help preserve the genetic diversity of giraffe subspecies and, when used for artificial inseminations, enhance genetic exchange between isolated populations. However, to date, the post-thaw motility of recovered sperm has been low and inconsistent. In this study, epididymal sperm collected from the testes of giraffes (n = 7) was frozen in three different extenders, namely, BotuCrio, Steridyl, and test egg yolk (TEY), each supplemented with one of two different cryoprotectants (5% glycerol or a mix of 1% glycerol and 4% methylformamide) and frozen over liquid nitrogen vapor. Across all three extenders, sperm showed significantly better post-thaw results when frozen with a mix of glycerol and methylformamide compared with glycerol alone. Sperm frozen with TEY and a mix of glycerol and methylformamide achieved superior post-thaw total and progressive sperm motility of 57 ± 3% and 45 ± 3%, respectively. These results show the benefit of using alternative cryoprotectants for freezing giraffe spermatozoa and could aid in the application of ARTs for giraffe subspecies or the closely related endangered Okapi.

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.