Comparative analysis of in vitro characteristics of fresh and frozen-thawed urethral and epididymal spermatozoa from cats (Felis domesticus)

Abstract

The first aim of this study was to provide a comprehensive analysis of structural and functional features of spermatozoa in semen collected from the same cat by two methods: urethral catheterization and epididymis slicing. The second aim was to assess if feline urethral (CT) and epididymal (EP) spermatozoa undergo the same changes during cryopreservation and to compare the postthaw characteristics of spermatozoa collected by the two methods. In the first phase, CT and EP semen were collected from 20 cats, and sperm motility, viability, morphology, computer-assisted sperm analysis (CASA) parameters, membrane and acrosome integrity, mitochondrial potential, lipid peroxidation, and chromatin status were assessed. In the second phase, both types of semen collected from 10 cats were cryopreserved, thawed, and the same sperm parameters were assessed as in fresh semen. Fresh CT spermatozoa (phase I) showed higher (P < 0.05) motility (subjective: median 75.0% vs. 62.5%; by CASA: mean ± SD 60.2 ± 10.7% vs. 43.1 ± 16.7%), morphology (mean ± SD, 57.5 ± 9.6% vs. 45.2 ± 15.9%), and membrane integrity (median live: 89.2% vs. 79.8%). Other parameters were not different between CT and EP spermatozoa. After cryopreservation (phase II), spermatozoa from both types of semen did not differ significantly, except for lipid peroxidation of live sperm cells (median CT: 3.5%, EP: 1.7%, P < 0.05). Urethral and EP spermatozoa showed a similar, significant drop in motility (CT to 18.6 ± 10.3% and EP to 21.6 ± 12.1%, P < 0.05), progressive motility (CT to 6.8 ± 5.9% and EP to 8.3 ± 8.8%, P < 0.05), and rapid movement (from 34.3 ± 20.6% to 8.5 ± 7.0% in CT and from 26.0 ± 14.7% to 10.1 ± 10.4% in EP, P < 0.05), whereas other motion characteristics assessed by CASA were not affected (P > 0.05). The strongest change after cryopreservation was noted in high mitochondrial potential (median CT: 1.3%, EP: 2.2%). Although cryopreservation increased acrosome damage and lipid peroxidation, the level of these changes in the population of live sperm cells remained low (median acrosome damage: CT: 3.3%, EP: 4.5%, lipid peroxidation CT: 3.5%, EP: 1.7%). Cryopreservation did not affect chromatin structure (median percent DNA fragmentation index, CT: 3.3%, EP: 2.3%). In this study, we confirmed that urethral catheterization for collection of semen allows the retrieval of spermatozoa with quality equally good as in those obtained by epididymal slicing. Spermatozoa from both types of semen collected showed similar characteristics after freezing/thawing so both types can be used for semen banking.