Abstract
In order to protect the spermatozoa against cold shock, hen egg yolk is widely used as a cryoprotective agent in semen freezing extenders for domestic animals. The protective action of yolk is largely presumed to be due to low density lipoproteins (LDL). The effects of LDL on sperm quality of bull and northern pike (Esox lucius) after freezing-thawing have been reported, but no study has been made to evaluate the effect of LDL on boar sperm motility and other characteristics. The experiment was carried out to investigate the effect of LDL on the freezing of boar sperm in 0.25 ml straws. The aim was to evaluate the quality of boar spermatozoa cryopreserved in the presence of LDL. Motility of semen cryopreserved in LDL was analyzed and compared to semen cryopreserved with Tris-citric acid-glucose (TCG) and Tris-citric acid-fructose (TCF), two basic freezing extenders containing egg yolk. Similarly, acrosome and plasma membrane integrity were also evaluated and compared to semen cryopreserved with TCG and TCF. Analysis of sperm quality after freeze-thaw showed that the motility, acrosome and plasma membrane integrity were improved with LDL in the extender, as compared to the TCG and TCF. The highest post-thaw integrity of acrosome and plasma membrane and motility were obtained with 9% LDL (w/v). Consequently, the optimum LDL concentration in the extender was 9%. It is also suggested that the concentration of LDL addition is important for the effect on boar sperm protection during freezing and thawing. The percentage of motile spermatozoa was significantly higher after freezing in 9% LDL than in TCG and TCF 54.4% versus 30.4% and 30.1% (p<0.05), respectively. The integrity of acrosome and plasma membrane were also significantly higher at 70.3% and 50.5% respectively with semen frozen in 9% LDL extender compared to TCG at 37.8% and 30.3% and TCF at 36.4% and 29.9%, respectively (p<0.05),. In conclusion, we propose that extender containing LDL extracted from hen egg yolk could be used as a cryoprotective media with a better efficiency than TCG and TCF. LDL improved boar semen quality, allowing better spermatozoa motility, acrosome and plasma membrane integrity after the freeze-thaw process. Furthermore, we found out that the extender with 9% LDL concentration significantly enhanced motility, acrosome and plasma membrane integrity of boar sperm after freezing and thawing. (Asian-Aust. J. Anim. Sci. 2006.
Highlights
Artificial insemination (AI) is an important tool for distribution of the genetic potential of males, the aim of sperm freezing is the production of a bank of sperm cells to be used for it
The structure of the low density lipoproteins (LDL) is based on a triglyceride core surrounded by a film of proteins and phospholipids having their polar residues in contact with the aqueous phase (Cook et al, 1969)
The respective precise role of lipids and apoproteins on the cryoprotective action of LDL were not clearly established, the previous experiments affirmed that the LDL fraction was responsible for the cryoprotective effect of egg yolk during freeze-thaw processing of mammalian spermatozoa (Polge et al, 1970; Evans et al, 1973; Demianowicz and Strezek, 1996; Trimeche et al, 1996)
Summary
Artificial insemination (AI) is an important tool for distribution of the genetic potential of males, the aim of sperm freezing is the production of a bank of sperm cells to be used for it. AI is the reproductive biotechnology which has been widely used for genetic improvement, and most of the semen has been frozen. Various biochemical and anatomical compartments in the spermatozoa cells may be altered during freeze-thaw process, and the current methods for cryopreservation of boar spermatozoa are unsatisfactory. They have poorer motility , acrosomal morphology and viability than fresh sperm
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