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Background  Sperm selection methods such as Single Layer Centrifugation (SLC) have been demonstrated to be a useful tool to improve the quality of sperm samples and therefore to increase the efficiency of other artificial reproductive techniques in several species. This procedure could help to improve the quality of genetic resource banks, which is essential for endangered species. In contrast, these sperm selection methods are optimized and focused on farm animals, where the recovery task is not as important as in endangered species because of their higher sperm availability. The aim of this study was to evaluate two centrifugation methods (300 x g/20 min and 600 x g/10 min) and three concentrations of SLC media (Androcoll-Bear −80, 65 and 50%) to optimise the procedure in order to recover as many sperm with the highest quality as possible. Sperm morphology could be important in the hydrodynamic relationship between the cell and centrifugation medium and thus the effect of sperm head morphometry on sperm yield and its hydrodynamic relationship were studied.    Results  The samples selected with Androcoll-Bear 65% showed a very good yield (53.1 ± 2.9) although the yield from Androcoll-Bear 80% was lower (19.3 ± 3.3). The latter showed higher values of motility than the control immediately after post-thawing selection. However, both concentrations of colloid (65 and 80%) showed higher values of viable sperm and viable sperm with intact acrosome than the control. After an incubation of 2 h at 37 °C, the samples from Androcoll-Bear 80% had higher kinematics and proportion of viable sperm with intact acrosome. In the morphometric analysis, the sperm selected by the Androcoll-Bear 80% showed a head with a bigger area which was more elongated than the sperm from other treatments.    Conclusions  We conclude that sperm selection with Androcoll-Bear at either 65% or 80% is a suitable technique that allows a sperm population with better quality than the initial sample to be obtained. We recommend the use of Androcoll-Bear 65% since the yield is better than Androcoll-Bear 80%. Our findings pave the way for further research on application of sperm selection techniques to sperm banking in the brown bear.    Electronic supplementary material  The online version of this article (doi:10.1186/s12917-017-1124-2) contains supplementary material, which is available to authorized users.

Improving sperm banking efficiency in endangered species through the use of a sperm selection method in brown bear (Ursus arctos) thawed sperm