One Number to Rule Them All: The Wildlife Sperm Index for Standardized Gamete Assessment

In wildlife conservation, breeding programs focused on reintroduction are critical to recovering endangered species. Assisted reproductive technologies (ARTs) and biobanking play pivotal roles in these efforts but depend on high-quality gametes. Spermatozoa, due to their structural simplicity and well documented quality assessments are often considered the preferred cell type for cryopreservation and ARTs, especially in rare or exotic species. However, inconsistent retrieval of sperm samples with sufficient volume and concentration, especially for critically endangered species, can pose major limitations to assessing overall sperm quality. To address this information gap, we have developed the Wildlife Sperm Index (WSI), a standardized scoring system that integrates key sperm quality metrics--such as motility, viability, and DNA integrity--into a weighted composite score. While this study applies the WSI to sperm, the framework is adaptable to other cell types used in biobanking and reproductive technologies, broadening its potential utility. Unlike traditional sperm assessments that rely solely on microscopy, the WSI provides a scalable and quantitative framework for evaluating samples across species, including those that yield low-volume or concentration sperm samples. We validated the WSI against traditional means of sperm quality assessments, demonstrating its reliability as both a quality assessment and decision-making tool, enabling users to evaluate sample suitability for cryopreservation, ARTs, or downstream applications. By enabling standardized quality tracking, the WSI provides a foundation for more informed reproductive decisions to support global conservation efforts. Summary sentenceWe present the Wildlife Sperm Index (WSI), a standardized, composite scoring system that integrates key sperm quality metrics to improve gamete assessment and supports assisted reproduction and biobanking in wildlife conservation.