Effect of the addition of egg yolk to skim milk extender and cold shock on ram coated spermatozoa under cold liquid storage

This experiment was conducted to determine the effect of egg yolk levels and cold shock on coated spermatozoa by using 2 × 5 factorial arrangement of the ten treatments and 5 replicates under a repeated measure randomize design. At 5 sessions, semen was collected from three ram by artificial vagina contact with a tube containing Tris- fructose-egg yolk 15%. Samples were pooled, centrifuged and removed supernatant. Aliquot was split into two groups and each one was split into 5 subgroups and after that it was added egg yolk 0, 5, 10, 15 and 20%. First group was encountered with cold shock and second group was gradually cooled up to 5◦C then samples were incubated for 72 h. Progressive sperm motility, plasma membrane integrity, viability (by Hoechst 33258 fluorescent staining) and acrosome reaction (by PNA-Alexa flur-488) were investigated at 0, 24, 48 and 72 h. Sperm viability under cold shock and gradual cooling was higher in 5% egg yolk (67.6 ±1.47and 77.3±1.47, respectively) than 0% egg yolk (59.75±1.47 and 71.2±1.47, respectively). Sperm progressive motility, plasma membrane and acrosome integrity were improved in present of egg yolk; but, there was no difference among the treatments containing egg yolk. It was suggested that 5% egg yolk was superior to keep the function of ram coated spermatozoa for storage at 5ºC in skim milk extender.