95 EFFECT OF CRYOPROTECTANT ADDITION AND REMOVAL AT 4°C ON MOTILITY AND PLASMA MEMBRANE INTEGRITY OF BOVINE CAUDAL EPDIDYMAL SPERMATOZOA

Abstract

Cryopreservation of spermatozoa harvested from the epididymides would be a means of salvaging germplasm from genetically valuable males that die unexpectedly from injury, disease, or poaching. It is well known that the addition of cryoprotective agents (CPAs) is essential for sperm survival following the freezing process. However, CPAs can cause loss in sperm viability due to osmotic damage or chemical toxicity. The objective of this study was to determine the effects of single-step addition and/or removal of glycerol (GLY) or ethylene glycol (EG) on motility and plasma membrane integrity of bovine epididymal spermatozoa. Paired testes were obtained from mature bulls (n = 10) at a local abattoir and transported to the laboratory at 25–28°C within 4–6 h post-mortem. Epididymal spermatozoa were harvested by multiple incisions from the caudae epididymides of each bull, pooled, and washed in Brackett-Oliphant medium by centrifugation for 5 min at 500g. Pellets were resuspended in egg yolk-Tris-glucose-citric acid monohydrate medium (EYT-GC) at a concentration of 120 × 106 cells/mL and cooled to 4°C at a rate of 0.1°C/min. Specimens were allocated to each of five treatment groups: control (no CPA), 7% GLY, and 14% GLY, 7% EG, 14% EG. Then, replicate samples were diluted 1:1 in EYT-GC medium containing twice the final desired concentration of CPA. After being exposed for 10 min, each sample was diluted directly into EYT-GC at 4°C. Motility was assessed by means of a computer assisted semen analysis system and plasma membrane integrity was determined by SYBR 14 and propidium iodide staining followed by fluorescence microscopy. Differences among treatments were analyzed using one way ANOVA (P < 0.05). The results (Table 1) show that maximum survival, as assessed by measurements of motility and membrane integrity, was achieved with spermatozoa exposed to 7% EG. Almost identical intermediate levels of survival were observed with spermatozoa exposed to 7% GLY or 14% EG. The lowest survival was observed for spermatozoa exposed to 14% GLY. The results indicate that the use of EG as a cryoprotectant may minimize toxicity and osmotic damage to fresh bovine epididymal spermatozoa. Its efficacy as a CPA is currently being determined. Table 1. Sperm motility and membrane integrity (mean ± SEM) after addition of CPA to epididymal sperm