Comparison of two different cryopreservation protocols for freezing goat semen.

In this study, two different semen cryopreservation protocols were compared to freeze goat semen. The ejaculates (n=12) were collected by using electro-ejaculator from six mature bucks (two ejaculates per each buck). Each ejaculate was divided into two groups as Protocol 1 (P1) and Protocol 2 (P2). In P1, semen was diluted directly in an extender containing 15% egg yolk, 300mM Tris, 28mM glucose, 95mM citric acid 5% glycerol to a concentration of 200×10(6)sperm/mL. In P2, after the removal of seminal plasma by centrifugation, the semen sample was diluted with the first portion of milk extender consist of 100mg/mL skimmed milk powder and 27.75mM glucose (without glycerol) to a concentration of 400×10(6)sperm/mL. The second portion of the milk extender containing 14% glycerol was added to semen gradually in order to achieve sperm concentration 200×10(6)sperm/mL and 7% glycerol level in the final volume. Extended semen was loaded in 0.25mL straws, held for 2h at 4°C, frozen in nitrogen vapor and stored in liquid nitrogen. Post-thaw motility and live sperm rate (mean±SEM) were significantly lower (P<0.05) in P1 as compared to P2 (47.50±1.23% vs. 55.63±1.72%; 80.04±1.29% vs. 84.04±1.08%, respectively). However, live intact, total intact, abnormal, reacted acrosome and DNA damaged sperm rates were similar (P>0.05) in both protocols. It was concluded that both protocols used in this study provided reasonable post-thaw parameters; however, P2 yielded better motility and live sperm rate compared to P1.