Cryoconservation of animal genetic resources

Cryoconservation of animal genetic resources is a strategy wherein samples of animal genetic materials are preserved cryogenically.^[1]

Animal genetic resources, as defined by the Food and Agriculture Organization of the United Nations, are "those animal species that are used, or may be used, for the production of food and agriculture, and the populations within each of them. These populations within each species can be classified as wild and feral populations, landraces and primary populations, standardised breeds, selected lines, varieties, strains and any conserved genetic material; all of which are currently categorized as Breeds."^[2] Genetic materials that are typically cryogenically preserved include sperm, oocytes, embryos and somatic cells.^[3][4] Cryogenic facilities are called gene banks and can vary greatly in size usually according to the economic resources available. They must be able to facilitate germplasm collection, processing, and long term storage, all in a hygienic and organized manner. Gene banks must maintain a precise database and make information and genetic resources accessible to properly facilitate cryoconservation.^[1] Cryoconservation is an ex situ conservation strategy that often coexists alongside in situ conservation to protect and preserve livestock genetics.^[5]

Cryoconservation of livestock genetic resources is primarily done in order to preserve the genetics of populations of interest, such as indigenous breeds, also known as local or minor breeds. Material may be stored because individuals shared specific genes and phenotypes that may be of value or have potential value for researchers or breeders. Therefore, one of the main goals remains preserving the gene pool of local breeds that may be threatened.^[6] Indigenous livestock genetics are commonly threatened by factors such as globalization, modernization, changes in production systems, inappropriate introduction of major breeds, genetic drift, inbreeding, crossbreeding, climate change, natural disasters, disease, cultural changes, and urbanization.^[7][8][9] Indigenous livestock are critical to sustainable agricultural development and food security, due to their: adaptation to environment and endemic diseases, indispensable part in local production systems, cultural significance, and importance to local rural economies.^[4][9] The genetic resources of minor breeds have value to the local farmers, consumers of the products, private companies and investors interested in crossbreeding, breed associations, governments, those conducting research and development, and non-governmental organizations.^[1][10] Therefore, efforts have been made by national governments and non-governmental organizations, such as The Livestock Conservancy, to encourage conservation of livestock genetics through cryoconservation, as well as through other ex situ and in situ strategies.^[7][11] Cryogenic specimens of livestock genetic resources can be preserved and used for extended periods of time.^[12] This advantage makes cryoconservation beneficial particularly for threatened breeds who have low breed populations. Cryogenically preserved specimens can be used to revive breeds that are endangered or extinct, for breed improvement, crossbreeding, research and development. However, cryoconservation can be an expensive strategy and requires long term hygienic and economic commitment for germplasms to remain viable.^[1] Cryoconservation can also face unique challenges based on the species, as some species have a reduced survival rate of frozen germplasm.^[3][13][14]