- [Show abstract] [Hide abstract] ABSTRACT: We evaluated combinations of two commercial semen extenders and three concentrations of glycerol to determine the combination that yielded the highest post-thaw sperm motility. A randomised 2 x 3 block design was used. Semen was collected from four stallions (6 collections per stallion). The sample was diluted with either a dried skim-milk glucose extender (EZ Mixin Original Formula) or a chemically defined, milk-free diluent (INRA 96), and each was used in combination with 2%, 3% or 4% glycerol in standard commercial freezing medium. Sperm motility was assessed by microscopy in fresh and post-thaw semen. There was a significant difference between the two extenders in the motility of spermatozoa after cryopreservation (48.9% for INRA 96; 38.6% for EZ Mixin OF; P < 0.0001). Glycerol at 4% in freezing medium yielded the highest post-thaw motility, significantly better than 2% (P < 0.05). Three of four stallions had significantly higher post-thaw motility using INRA 96 relative to EZ Mixin OF (P < 0.01), and two of four stallions had significantly higher post-thaw motility using 4% glycerol (P < 0.05). The combination of INRA 96 and 4% glycerol in freezing medium gave the highest average post-thaw motility of 51.5%. In this study, INRA 96 combined with 4% glycerol yielded an average recovery of progressively motile sperm consistently above the 35% target.
- [Show abstract] [Hide abstract] ABSTRACT: After cryopreservation, spermatozoa from many stallions may have a lower capacity to fertilize an oocyte than fresh or cooled semen. The aim of this study was to evaluate a standard panel of semen extenders and varied concentrations of the cryoprotective agent (glycerol) to optimize sperm survival rates after cryopreservation. Semen was collected from Quarter Horse stallions (n = 3) from March to May 2006 (6 collections per stallion). Semen was filtered immediately after collection, and sample volume and sperm concentration were measured. A drop of raw semen was placed on two prewarmed slides to estimate the percentage of progressively motile sperm. The semen sample was then diluted to 100 × 106 spermatozoa/mL with a dried skim milk glucose extender (EZ Mixin Original Formula; ARS, Chino, CA, USA) or a chemically defined, milk-free diluent (INRA 96; IMV, Maple Grove, MN, USA). After 1 h of slow cooling and equilibration to 4°C, semen samples were centrifuged for 10 min at 400g. A defined volume of supernatant was removed, so that a concentration of 1000 × 106 spermatozoa/mL was obtained after resuspension of the sperm pellet. A 150-µL aliquot of semen was then added to specified quantities of the same semen extender used after semen collection and cryopreservation medium (Cryoguard®; Minitube, Verona, WI, USA) to obtain final glycerol concentrations of 2, 3, and 4%. This also gave a concentration of 100 × 106 spermatozoa/mL. After equilibration for 1 h at 4°C, spermatozoa were loaded into 0.5-mL straws and frozen in liquid nitrogen vapor. After 10 min, straws were plunged into liquid nitrogen. Semen was thawed at 37°C for 30 s and evaluated as prior to cryopreservation. Mean total semen volumes were 56, 11, and 60 mL in the 3 stallions. Their respective mean sperm concentrations were 124 × 106, 505 × 106, and 161 × 106 sperm/mL, respectively. Mean percentages of progressively motile sperm prior to cryopreservation were 64, 89, and 72%, respectively. With the paired Student's t-test, percentages of progressively motile sperm after cryopreservation were evaluated with respect to semen extender and concentration of glycerol used. Mean overall progressive motility of spermatozoa after cryopreservation differed significantly between the two extenders and was 46% for INRA 96 and 35% for EZ Mixin OF (P < 0.001). Using EZ Mixin OF as semen extender, the best mean post-thaw progressive motility was achieved with 4% glycerol (39%) and differed significantly from that with 2% glycerol (32%; P < 0.01). When INRA 96 was used (49% for 4%, and 42% for 2% glycerol), there was no difference. This results provide evidence that, during freezing of equine spermatozoa, there is a significant effect of the semen extender and the concentration of the cryoprotectant on post-thaw sperm motility. We therefore suggest mini-freezing trials prior to freezing large numbers of sperm to find the semen extender and glycerol concentration that provides optimal survival rates.