Improving cryo-conservation through tissue conditioning to optimise survival after cryopreservation of ovarian tissues for endangered species

Project Details


Fertility preservation through ovarian tissue cryopreservation and viable biobanking has emerged as a crucial technique for safeguarding reproductive potential in various mammalian species, including humans and endangered wildlife. The Rhino Fertility Project established at Oxford relies on cryopreserved ovarian tissues, however, optimisation of viability of ovarian tissue following cryopreservation has never been carried out for any species, let alone non-model species. Recently, the Williams group demonstrated that delaying cryopreservation of sheep ovaries actually supported oocyte viability post cryopreservation and hypothesised that this was due to slowing the metabolism before the tissue was exposed to cryoprotective agents (CPAs), which are toxic. Thus, further work is essential to understand the mechanisms behind this improvement cryopreservation protocol and if this is replicated in other mammalian species, so we can better cryopreserve ovarian tissue for conservation. Current protocols used for human ovarian tissue cryopreservation result in the loss of 20-50% of oocytes, with woefully little knowledge about other species.


1. Investigate how delayed cryopreservation affects ovarian tissue viability and oocyte survival in different mammalian taxa.
2. Develop and refine cryopreservation protocols tailored to the specific needs of different mammalian taxa, considering factors such as tissue structure and metabolism.


Experiments will use various species to ascertain if increased viability is due to decreasing metabolism before tissues is exposed to CPA due to limited availability and appropriate use of a precious resource.

Metabolism will be determined by analysis of cell proliferation and metabolites. Ovarian tissues will be stored at 4°C for 12, 24 and 48 hours before dissection and cryopreservation of the ovarian cortex. Samples will be analysed at time 0, before freezing, and post thaw. We will use a multi-dimensional approach, including histological analysis, cell apoptosis, and functional assays to determine tissue viability.

After analyses have been carried out in domestic species, we will extend our analysis to non-domestic species using samples collected from non-domestic species as part of the collaboration with Chester Zoo and Nature’s SAFE.

CASE partner contribution

Chester Zoo is a partner of Nature’s SAFE (UK biobanking Charity), and provides samples for cryopreservation by Nature’s SAFE when animals at the zoo either die or are euthanased. This project will involve collection and processing of samples at Chester Zoo where a Nature’s SAFE hub is being established. Chester Zoo also has an active reproductive research programme with is led by Dr. Sue Walker.

Expected Impact

Improved understanding of ovarian tissue cryopreservation in wildlife species will enhance conservation efforts by providing a viable method for preserving genetic diversity and combating species decline by preserving these samples in the most appropriate manner to best preserve viability. The project's results can inform the development of guidelines and policies related to ovarian tissue cryopreservation in different mammalian taxa, ensuring ethical and practical considerations.


This project aims to address a critical knowledge gap in the field of fertility preservation and conservation biology by investigating how delayed cryopreservation affects ovarian tissue viability across diverse mammalian taxa. By optimising cryopreservation protocols and understanding species-specific variations, this research has the potential to impact clinical practice, wildlife conservation, and technological innovation. Ultimately, it contributes to our ability to safeguard reproductive potential and genetic diversity in a wide range of mammalian species, benefiting both humans and the natural world.

Please contact Suzannah Williams on if you are interested in this project.  The CASE partner supervisor will be Dr. Sue Walker, Chester Zoo, on