Cryopreservation of epididymal alpaca (Vicugna pacos) sperm: a comparison of citrate-, Tris- and lactose-based diluents and pellets and straws

Abstract

Epididymal spermatozoa were harvested from male alpacas and frozen after extension and cooling to 4°C in citrate-, Tris- and lactose-based diluents (Experiment 1) and as pellets in 0.25- and 0.5-mL straws on either dry ice or over liquid nitrogen vapour (Experiment 2) to determine the effects diluents and packaging on their motility and acrosome integrity. In Experiment 1, sperm motility was higher after cooling to 4°C and after freeze–thawing (0 but not 3 h post-thaw) for spermatozoa extended in the lactose- than the citrate- or Tris-based diluent (P < 0.05). Post-thaw acrosome integrity after cooling to 4°C and post-thaw (0 h) was reduced for spermatozoa frozen in citrate- compared with lactose- or Tris-based diluents, but was similar for all groups 3 h after thawing. In Experiment 2, sperm motility immediately after thawing was higher for pellet freezing than for 0.25- or 0.5-mL straws on dry ice or liquid nitrogen vapour (P < 0.05), although by 3 h post-thaw motility was similar for pellets and straws (P > 0.05). Acrosome integrity was similar for all groups immediately after thawing and 3 h post-thaw. Cryopreservation of epididymal alpaca spermatozoa is feasible, with retained motility and acrosome integrity post-thaw. Freezing as pellets in a lactose-based diluent is recommended.