Effect of egg yolk levels and equilibration periods on freezability of Jamunapari buck semen

Abstract

Semen ejaculates from adult Jamunapari bucks (2–4 year-old) maintained at the Central Institute for Research on Goats, Makhdoom (UP) were utilized for a study to find out the freezability of buck semen at different levels of egg yolk during different hours of equilibration period by conventional freezing protocol. The ejaculates were extended to maintain sperm concentration approximately 100 million per dose (0.25 ml) in Tris-Citric Acid- Fructose (TCF) diluent having 0, 5, 10, 15 and 20% (v/v) egg yolk and 6% (v/v) glycerol as a cryoprotectant. Filling and sealing of straws were done at 5oC in cold handling cabinet after 2, 3, 4 and 5 h of equilibration period followed by vapour freezing of straws for 10 min at 2 cm above the liquid nitrogen and finally plunged into liquid nitrogen. Post-thaw motility, live sperm count, sperm abnormalities, acrosomal integrity and hypo-osmotic swelling test were conducted to assess freezability. The post-thaw motility, live sperm count, abnormalities, acrosomal integrity and hypo-osmotic swelling (HOS) positive spermatozoa differed significantly (P<0.05) at different levels of egg yolk and equilibration periods. Our results indicated that 10% egg yolk and 4 h of equilibration period is the best combination for semen freezing. The overall results showed that the inclusion of egg yolk significantly improved sperm post-thaw motility, indicating its beneficial effects during the freezing steps of cryopreservation. Furthermore, neither glycerol nor egg yolk alone protected the acrosome and tail membrane; the combination of two significantly (P<0.05) reduced the proportion of acrosome-damaged spermatozoa.