Comparison of different diluents based on liposomes and egg yolk for ram semen cooling and cryopreservation

摘要

Background: Sperm cryopreservation is an important tool for breed improvement, nonetheless, spermatozoids of rams are extremely sensitive to cryopreservation. Aims: The present research was to compare a liposome-based (OptiXcell: OX) diluent, a commercial TRIS-egg yolk (Optidyl: OP) and a citrate egg yolk-based (CY) diluent on ovine semen quality through the cryopreservation process. Methods: Semen was collected from four sexually mature Dorper rams during the natural breeding season. After collection, semen was evaluated and diluted in OX, OP or CY diluent and was cooled from 37 degrees C to 4 degrees C for 2 h (refrigerated semen, RS), after that semen-filled straws were placed in liquid nitrogen (LN) vapour for 10 min, then immersed into LN at -196 degrees C (cryopreserved semen, CS) and stored until evaluation. Results: For fresh semen (FS), similar values (P>0.05) were obtained from the 3 diluents [motility (4.2 +/- 0.3), viability (75.4 +/- 3.2), hypo-osmotic swelling test (HOST) (59.2 +/- 2.1), and normality (84.7 +/- 3.5)]. The motility values were higher for RS with OX and CY (4.0 +/- 0.2 and 3.6 +/- 0.3, respectively) compared to OP (3.0 +/- 0.21; P 0.05), but for frozen semen, viability was lower in the CY diluent (P 0.05) but higher than in CY (48.7 +/- 1.5; P<0.05). Conclusion: No difference was found between the OX diluents and those made with egg yolk in terms of sperm parameters; however, the OX diluent was more efficient in protecting the integrity of membrane in freezing/thawing semen.