Study the Effect of Extracted Low-Density Lipoprotein from Egg Yolk on the Cryopreservation of Nguni Bull Semen

Abstract

The mechanism on how Egg Yolk (EY) helps sperm to survive the low temperature outside the animal body during cryopreservation and thawing process is not yet known. It is usually believed that the Low-Density Lipoprotein (LDL) is the major component that provides protection. The present study was undertaken to assess the cryo-protective effect of different concentrations (6, 8, 10 and 12%) of LDL and 20% EY (control) on sperm motility, morphological parameters and cleavage rate of the cows ovaries following freezing and thawing. Semen was collected from five Nguni bulls aged 2-4 years of known and proven fertility with an aid of electro-ejaculated and immediately transported to the laboratory. The LDL was extracted from the chicken egg yolk and further processed. The collected semen samples were evaluated for microscopic sperm motility and morphological parameters. Thereafter, the semen samples were diluted with different concentrations (6, 8, 10 and 12%) of LDL and 20% EY (control) extender supplemented with 12% Glycerol as a cryoprotectant. Semen samples were loaded into 0.25 straws, placed into a controlled rate programmable freezer and stored in liquid nitrogen tank. Following semen thawing, sperm motility, morphological were evaluated. Furthermore, In vitro fertilization (IVF) was conducted on cow’s oocytes to test the fertilizing ability of semen diluted with LDL on the cleavage rate. Data was analyzed with the aid of ANOVA. Furthermore, treatment means were compared with the Least Significance Difference (LSD) test. The percentage of motility parameters and percentage of live sperm with intact plasma membrane, acrosome membrane and DNA integrity were significantly higher (P<0.05) in semen diluted with 20% EY (control) and 8% compared to semen diluted with 6, 10 and 12% LDL). Cleavage rates were significantly higher (P<0.05) higher in extender containing 20% EY (control) and 8% LDL. In conclusion, 8% LDL extender can be used as an alternative to 20% EY extender in preserving the sperm motility rate, percentage of live sperm, intact plasma membrane, acrosome, DNA integrity and fertilizing ability of frozen-thawed Nguni bull semen.