12 COMPUTER-ASSISTED SPERM ANALYSIS OF FRESH EPIDIDYMAL CAT SPERMATOZOA AND THE IMPACT OF COOLED STORAGE (4°C) ON SPERM QUALITY

Abstract

Feline epididymal sperm is commonly used for in vitro fertilization. It also yields the opportunity to conserve genetic material from valuable males that suddenly die. Epididymal sperm quality parameters vary considerably among laboratories, implicating the need for objective evaluation methods. The aim of the present study was to describe reference values of computer-assisted sperm analysis (CASA) parameters of fresh epididymal cat sperm and to assess the effect of prolonged cooled storage (4°C) on various sample characteristics. Epididymides obtained from tomcats after routine orchiectomy (2–4 pairs/replicate) were sliced to release spermatozoa. The sperm suspension was placed on a 2-layer gradient and, after centrifugation, the sperm pellet was recovered. In Experiment 1 (20 replicates), sperm motility parameters were assessed immediately after retrieval (T0) using the Hamilton Thorne analyzer Ceros 12.1 (HTR; Hamilton Thorne Biosciences, Beverly, MA, USA). In Experiment 2, fresh (T0) sperm samples (4 replicates) were evaluated for motility parameters (HTR), acrosomal status (FITC-Pisum sativum agglutinin staining), morphology (eosin/nigrosin (E/N) staining), and membrane integrity (E/N and SYBR^®-14-propidium iodide staining; Molecular Probes, Inc., Eugene, OR, USA). After addition (1:2) of a Tris-glucose-citrate diluent containing 20% egg yolk, samples were cooled and reassessed on Days 1 (T1), 3 (T3), 5 (T5), 7 (T7), and 10 (T10). Results were analyzed in a mixed linear model, with replicate as random factor and time as fixed effect (S-PLUS 7.0; Insightful Corp., Seattle, WA, USA). Results of Experiment 1 were as follows (mean ± SD): motility (MOT): 80.8% ± 23.5; progressive motility (PMOT): 69.9% ± 23.2; velocity average pathway (VAP): 98.7 µm s^–1 ± 24.2; velocity straight line (VSL): 89.3 µm s^–1 ± 25.4; velocity curved line (VCL): 134.8 µm s^–1 ± 31.9; amplitude lateral head (ALH): 4.3 µm ± 2.0; beat cross frequency (BCF): 34.6 Hz ± 7.0; and straightness (STR): 89.6% ± 6.6. In Experiment 2, MOT, PMOT, VAP, VSL, VCL, BCF, and the percentage of normal spermatozoa showed a decrease over time (P < 0.05) compared to fresh samples, starting from T1, T3, T5, T7, T5, T3, and T1, respectively. In contrast, STR, ALH, membrane integrity, and the percentage of acrosome-intact spermatozoa were not affected (P > 0.05) by cooled storage. To summarize, we have presented a set of reference values for CASA-parameters of fresh, epididymal cat spermatozoa. Cooled storage impaired most motility parameters and lowered the percentage of normal spermatozoa, but did not influence membrane integrity or acrosomal status. The effect of cooled storage on DNA fragmentation of sperm and its subsequent influence on in vitro embryo development require further investigation.