Effects of vitrification on ram spermatozoa using free-egg yolk extenders

The present study aimed to examine the behavior of ram spermatozoa subjected to a vitrification process in free-egg yolk diluents in relation with conventional diluents and cryopreservation protocol used in this species. Previously it was investigated the toxicity of cryoprotectants, sucrose and glycerol, based on different concentrations (sucrose at 0.03 M, 0.05 M, 0.15 M and 0.25 M; and glycerol at 3%, 7%, 14% and 18%) compared to a commercial extender (Biladyl® with 20% egg yolk and 7% glyerol). Cryoprotectants which reported less toxicity were chosen to perform the vitrification and results were compared with the conventional cryopreservation. Semen from three rams was collected by electroejaculation. The sperm evaluation was carried out at 0, 2 and 4h through the incubation time at 37°C for the experiment of toxicity and, at thawing when cryopreservation was performed. The sperm quality throughout the incubation time always resulted lower (P⩽0.05) for the free-egg yolk diluents in relation to Biladyl® (control), obtaining the lowest values of sperm quality with the highest concentrations of sucrose and glycerol. The vitrification was carried out with combinations of sucrose and glycerol (sucrose at 0.03 and 0.05 M with 3% and 7% of glycerol, respectively) and with Biladyl® (at different sperm concentrations). The vitrification decreased drastically (P⩽0.05) the sperm quality when combinations of sucrose and glycerol were used. Nevertheless, the sperm samples vitrified with Biladyl® at the lowest sperm concentration showed acceptable values of viability, acrosome integrity and DFI, although the sperm motility was strongly decreased. In conclusion, the use of vitrification with diluents based on combinations of sucrose and glycerol did not work for semen cryopreservation of ram. Promising results were obtained when diluents with egg yolk were used in the vitrification procedure, although more studies are necessary to improve this technique and the use of diluents without egg yolk.