Cryopreservation and post-thawed fertility of ram semen frozen in different trehalose concentrations.

We evaluated freeze-thawing tolerance of heterospermic ram spermatozoa (Pampinta breed) in a base diluent (Tris, citric acid, fructose, egg yolk, glycerol) with the addition of different trehalose concentrations (0-400 mOsm). We chose sperm motility, acrosome integrity and hypo-osmotic swelling test as parameters to evaluate cryopreservation capacity. We obtained the best results for 50 and 100 mOsm trehalose-supplemented extenders, with values (referred to fresh semen values) of 65% for motility, 75% for acrosome integrity and 50% for hypo-osmotic swelling test, while freeze-thawing tolerance diminished significantly for 200 and 400 mOsm of the disaccharide. Fertility values measured at lambing were 47.1 and 44.6% (2 consecutive years), using semen cryopreserved in 100 mOsm trehalose-containing diluent, which is 2.5 times greater than those obtained with the base diluent (18.5 and 14.5%). We conclude that the membrane-protecting disaccharide trehalose confers a greater cryoprotective capacity to the base extender, when added up to 100 mOsm. This action is reflected in the different sperm membranes, the motile activity and in vivo fertility.