Effect of different levels of egg yolk on ram sperm coating and preserving at 5°C

Experiment was conducted to evaluate the effect of different levels of egg yolk for coating and storing spermatozoa. Ejaculates were collected from four rams. In each session، second ejaculates (n=4) were collected in a tube containing 1 mL coating buffers which were prepared by 10، 15 or 20% egg yolk plus Tris-fructose. Samples were pooled، centrifuged and the supernatant removed in the laboratory. The pellets were diluted with Tris-fructose containing egg yolk which was equal to its concentration in coating. To perform four replicates for each sample، diluted sample was split into four parts then each part was split into two fractions. One of them (cold-shock) was suddenly put on ice water and the other was chilled at 0. 25°C/min until 5°C. Aliquots were kept at 5°C for 36 h and sperm motility، viability and functional membrane integrity were determined at 0، 12، 24 and 36 h. The results showed that functional membrane integrity was highest in 20% yolk egg under gradual cooling at 0، 24 and 36 h (85. 7، 75. 9 and 71. 7%،respectively; P<0. 05). In the presence of 20% egg yolk، sperm viability was highest under cold-shock (74. 8%) and gradual cooling (78. 5%) and sperm motility was lower in cold-shock than gradual cooling at all storage times (76. 9، 60. 7، 36. 2 and 27. 7% vs. 85. 4، 73. 1، 54. 6 and 40. 8%، respectively; P<0. 05). Therefore، 20% egg yolk can improve coated sperm longevity in normal gradual cooling; but it does not prevent the destructive effect of cold-shock from taking place.