‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬‬Comparison of frozen-thawed and lyophilized egg-yolk extenders for chilled canine semen preservation: A preliminary study

Few studies have evaluated lyophilized extenders for semen preservation. The objective of this proof-of-concept study was to evaluate the ability of a lyophilized and reconstituted fresh egg-yolk extender (L-FEY) to preserve chilled canine semen compared with a conventional frozen-thawed egg-yolk extender (FEY). Three independently prepared semen pools were divided between L-FEY and FEY, stored at 5 °C, and evaluated on Days 0, 2, 4, and 7. Total and progressive motility, curvilinear velocity (VCL), straight-line velocity (VSL), average-path velocity (VAP), sperm viability, and acrosomal integrity were assessed. Data were analyzed using two-factor repeated-measures ANOVA, with extender and storage time as within-subject factors. Total motility declined during storage in both groups, with closely overlapping values throughout the study. Progressive motility showed a significant extender × time interaction (P = 0.023); in FEY, it decreased from 28.6 ± 2.2% on Day 0 to 17.1 ± 2.8% on Day 7 (P = 0.016), whereas no pairwise differences among storage days were detected in L-FEY. VCL was unaffected by storage time, extender, or their interaction. VSL and VAP decreased with storage time (P = 0.009 and P = 0.047, respectively), but neither the extender effects nor interactions were significant. Storage time also affected viability and acrosomal integrity (P = 0.008 and P = 0.010, respectively), although no individual pairwise comparisons were significant. No overall extender effects were detected for the evaluated outcomes. These preliminary findings indicate that L-FEY can preserve motility, sperm velocity, viability, and acrosomal integrity during 7 days of storage at 5 °C without detectable overall impairment relative to FEY.