Reintroducing genetic diversity in populations from cryopreserved material: The case of Abondance, a French local dairy cattle breed

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Abstract
Background Genetic diversity is a necessary condition for populations to evolve under adaptation, selection or both. However, genetic diversity is often threatened, in particular in domestic animal populations where artificial selection, genetic drift and inbreeding are strong. In this context, cryopreserved genetic resources appear as a promising option to reintroduce lost variants and to limit inbreeding. However, while more common in plant breeding, the use of cryopreserved resources is less documented in animals due to a longer generation interval making it difficult to fill the performance gap due to continuous selection. Thus, this study investigates one of the only concrete cases presenting the results of the use of cryopreserved semen of a bull born in 1977 and belonging to a disappeared lineage, into the breeding scheme of a French local dairy cattle breed, the Abondance breed, more than 20 years later. Results We found that this re-used bull was very original relative to the current population and thus allowed to restore genetic diversity lost over time. The expected negative gap in milk production due to continuous selection has been absorbed in a few years by preferential mating with elite cows. Moreover, the re-use of this old bull did not increase the level of inbreeding, it even tended to reduce it by avoiding mating with relatives. Finally, the reintroduction of an old bull in the breeding scheme allowed for increased performance for reproductive abilities, a trait that was less subject to selection in the past. Conclusions The use of cryopreserved material was efficient to manage the genetic diversity of an animal population, by mitigating the effects of both inbreeding and strong selection. However, attention should be paid toward mating in order to limit the disadvantages associated with the provision of genetic originality, notably a discrepancy in the breeding values for selected traits or an increase in inbreeding. Therefore, a careful characterization of the genetic resources available in cryobanks could help to ensure the sustainable management of populations and of local or small ones in particular. These results could also be transferred to the conservation of wild populations.
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