Effect of glycerol concentration, Equex STM supplementation and liquid storage prior to freezing on the motility and acrosome integrity of frozen-thawed epididymal alpaca (Vicugna pacos) sperm.

Two experiments were conducted to determine the effects of glycerol concentration and Equex STM paste on the post-thaw motility and acrosome integrity of epididymal alpaca sperm. In Experiment 1, epididymal sperm were harvested from male alpacas, diluted, and cooled to 4 degrees C in a Lactose cooling extender, and pellet-frozen in a Lactose cryodiluent containing final glycerol concentrations of 2, 3, or 4%. In Experiment 2, epididymal sperm were diluted in Biladyl, cooled to 4 degrees C, stored at that temperature for 18-24 h, and further diluted with Biladyl without or with Equex STM paste (final concentration 1% v:v) before pellet freezing. In Experiment 1, sperm motility was not affected by glycerol concentration immediately (2%: 16.1 +/- 4.6%; 3%: 20.5 +/- 5.9% and 4%: 18.5 +/- 6.6%; P > 0.05) or 3h post thaw (< 5% for all groups; P > 0.05). Post-thaw acrosome integrity was similar for sperm frozen in 2% (83.6 +/- 1.6%), 3% (81.3 +/- 2.0%) and 4% glycerol (84.8 +/- 2.0%; P > 0.05) but was higher 3h post-thaw for sperm frozen in 3% (75.7 +/- 3.8%) and 4% (77.2 +/- 4.1%) than 2% glycerol (66.9 +/- 2.7%; P < 0.05). In Experiment 2, sperm motility was higher immediately after thawing for sperm frozen in the presence of Equex STM (Equex: 21.5 +/- 3.5%; control: 14.4 +/- 2.1%; P < 0.05) but was similar at 3h post-thaw (P > 0.05). Acrosome integrity was similar for sperm frozen with or without Equex STM paste immediately (control: 89.6 +/- 1.2%; Equex: 91.1 +/- 1.4%; P > 0.05) and 3 h post-thaw (control: 69.3 +/- 3.7%; Equex: 59.9 +/- 5.8%; P > 0.05). Sperm cryopreserved in medium containing 3-4% glycerol and 1% Equex STM retained the best motility and acrosome integrity, even after liquid storage for 18-24 h at 4 degrees C prior to cryopreservation. Copyright 2010 Elsevier Inc. All rights reserved.