Traditionally, egg yolk is a protective agent that is used to freeze semen in various species. However, the addition of egg yolk in extender risks the introduction of disease. Therefore, an alternative cryoprotective agent should be found to preserve ram semen. The aim of this study was to evaluate the effect of phosphatidylcholine (PC) as a protective agent in extender with or without egg yolk on semen characteristics and acrosome integrity of frozen then thawed Bapedi ram semen. Semen was collected from four mature Bapedi rams, in the Agricultural Research Council (ARC) Germplasm Conservation Programme, using an artificial vagina. Following collection, semen samples were randomly diluted into Tris-based extender (1: 2), with and without egg yolk, and supplemented with four concentrations of PC liposome (0 mg/ml), 0.25 mg/ml, 0.5 mg/ml and 0.75 mg/ml). Supplementation of PC liposome in extender with or without egg yolk did not improve the semen total motility (TM), progressive motility (PM) and rapid motility (RM) rate. The sperm cell membrane integrity in extender with or without egg yolk was not influenced by the supplementation of PC liposome after thawing (P >0.05). The addition of PC liposome to Tris-based extender with egg yolk had a similar result to control (Tris-based extender with egg yolk) on sperm cell acrosome integrity. In conclusion, supplementation of PC liposome to Tris-based extender without egg yolk had lower sperm cell viability and motility rates compared with the extender with egg yolk, regardless of concentration.Keywords: acrosome, cryoprotectant, liposome, membrane, motility

Traditionally, commercial hen egg yolk has been used in extenders or freezing media because of its easy availability. However, the use of quail egg yolk has not been used for preserving Nguni bull semen. The aim of the study was to compare the suitability of different quail egg yolk concentrations (5, 10, 15, and 20%) for cryopreserving Nguni bull semen. Semen was collected from 14 stud Nguni bulls with the aid of electro ejaculator. Collected semen samples were kept in a thermos-flask containing warm water at a temperature of 37°C and transported to the laboratory for further analyses. The sperm motility traits were evaluated using computer-aided sperm analysis prior extension. Semen samples were then randomly allocated into 5, 10, 15, and 20% of quail egg yolk and 20% concentration of chicken egg yolk (control) in citrate extender. The extender was supplemented with 12% of glycerol (Seshoka et al. 2012) as a cryoprotectant, and semen samples were diluted (1 : 2) and equilibrated for a period of 4 h at 5°C. After equilibration, semen samples were loaded into 0.25-mL straws, placed into a controlled rate programmable freezer, and stored in a LN tank (–196°C) until thawing. Frozen semen straws were thawed in a water bath at 37°C for 1 min. Thawed semen was evaluated for sperm motility traits using a computer-aided sperm analysis system. Data were analysed with ANOVA. A significant difference was recorded between fresh total sperm motility rate (99%) and frozen-thawed semen samples with either 5% (87.3%) quail or 20% (87.6%) chicken egg yolk citrate extender compared with 10% (92.6%), 15% (91.2%), or 20% (89.9%) quail egg yolk citrate extender. Moreover, fresh semen also resulted in a significantly higher progressive sperm motility rate (39.3%) as compared with frozen-thawed with 5% (26.2%) or 20% quail (28.5%) or 20% chicken (22.7%) egg yolk citrate extender. The results also demonstrated that the use of 10, 15, and 20% quail egg yolk in citrate extender yielded comparable results on total sperm motility with fresh semen as compared with 5% quail and 20% chicken egg yolk. In conclusion, quail egg yolk extender provided sufficient cryo-effectiveness to cryopreservation of Nguni bull semen.