RESUMEN
Semen banking is critical to preserving rare and autochthonous breeds. However, protocols can change with time, leaving heterogeneous semen batches. The objective of this study was to assess differences in sperm quality and field fertility. We report differences between batches frozen with the Biociphos and BIOXCell extenders in the Asturiana de la Montaña cryobank (autochthonous and endangered breed, Northern Spain). Doses from 48 bulls were analysed by CASA and flow cytometry. The 85-days non-return rates from AI records were used to assess the fertility of 23,853 AI. BIOXCell showed higher quality post-thawing. Differences increased after a 5-hr incubation at 37°C, and Biociphos yielded doses with lower resilience. Field fertility did not differ between extenders (Biociphos: 57.4% ± 1.2; BIOXCell: 56.6% ± 3.0), possibly because of AI protocols compensating for differences in quality. However, this needs to be confirmed by controlled intervention studies. In conclusion, batches frozen with Biociphos may require specific strategies for compensating for the lower sperm quality. Regular surveys and evaluation of cryobank procedures may be useful to characterizing stored batches and defining strategies to guaranteeing success in their future use.