Effect of warming temperatures on donkey sperm vitrification in 0.5 mL straws in comparison to conventional freezing

Aim of study: There is little information about vitrification of sperm in large volumes (up to 0.5 mL). This study aimed to develop the vitrification technique in 0.5 mL straws in donkey sperm, evaluating the effect of three warming temperatures.Area of study: Cordoba, Spain.Material and methods: Ejaculates from five donkeys were divided in four groups: one control subjected to conventional slow freezing (C) and three vitrified in 0.5 mL straws and warmed using different protocols (W1: 37ºC/30s, W2: 43ºC/20s and W3: 70ºC/8s+37ºC/52s). Sperm motility, kinematic parameters, plasma membrane and acrosome integrity were evaluated. Conventional freezing resulted in significantly higher values for total (42.7±19.6%), and progressive motility (30.3±16.7%), plasma membrane (49.1±10.4%) and acrosome integrity (39.6±14.5%) respect to vitrification method.Main results: Values after warming ranged between 0.2-2.8% for total motility; 0.2-2.1% for progressive motility; 5.5-20.0% for plasma membrane integrity and 14.5-29.8% for acrosome integrity in all warming protocols after sperm vitrification. However, no differences were found between W3 and C for kinematic parameters; and W3 resulted in significantly higher values for membrane integrity (20.0±11.0%) in comparison to W1 (5.5±3.6%) and W2 (9.3±8.4%).Research highlights: High warming rates seem to be better for donkey sperm vitrification in large volumes; but this methodology is still not an alternative to conventional sperm freezing