Abstract
Soybean lecithin has been attracted increasing attention and has been used to replace egg yolk in the cryopreservation of domestic animal semen. However, its effects on freezing boar spermatozoa have never been evaluated. In the present study, semen was collected from five Duroc boars and frozen-thawed in extender with different concentrations of soybean lecithin (3, 6, 9 and 12%) and 20% egg yolk. Semen parameters including sperm motion characteristics (the percentage of total motile sperm and motility), plasma membrane integrity and acrosome integrity were assessed with a computer-aided semen analysis (CASA) system, hypoosmotic swelling test (HOST) and fluorescein isothiocyanate-conjugated peanut agglutinin (FITC-PNA) method, respectively. The result best result was obtained for the extender supplemented with 6% soybean lecithin, with values of 59.7% for the percentage of total motile sperm (TM%), 44.3% for motility, 45.3% for plasma membrane integrity and 61.9% for acrosome integrity. TM%, motility, acrosome integrity and plasma membrane integrity in the extender containing 6% soybean lecithin were significantly higher than that of other concentrations of soybean lecithin and 20% egg yolk (P < 0.05). However, the percentages of TM, acrosome integrity and plasma membrane integrity decreased with the increasing concentration of soybean lecithin in extender. In summary, the effect of soybean lecithin on spermatozoa quality was superior and the effective concentration of soybean lecithin in extender was 6% (w/v). Soybean lecithin might replace egg yolk in extender in the cryopreservation of boar semen. Key words: Boar semen, cryopreservation, soybean lecithin, motility, acrosome integrity.
Highlights
Freezing of boar spermatozoa has been studied since 1956
The objective of the present study was to investigate the effects of soybean lecithin in different concentrations (3, 6, 9 and 12%) on sperm motion characteristics including percentage of total motile sperm, linear motile sperm and plasma membrane integrity and acrosome integrity compared with 20% egg yolk on boar sperm cryopreservation
The sperm motion characteristics, plasma membrane integrity and acrosome integrity were used as predictors for quality of frozen-thawed boar spermatozoa
Summary
Freezing of boar spermatozoa has been studied since 1956. current methods and freezing extenders for the cryopreservation of boar spermatozoa are unsatisfactory. Different to other domestic animals, boar sperm is extremely vulnerable to cold shock by sudden cooling and this is thought as one of the most important factors which limit the development of freezing of boar spermatozoa (Parks and Lynch, 1992). Egg yolk has been used for providing protection against cold shock in the cryopreservation of mammalian semen for over half a century. Previous studies had confirmed that boar semen could acquire a resistance to cold shock with the addition of 20% egg yolk (Westendorf et al, 1975; Johnson et al, 2000). Low density lipoprotein (LDL) extracted from egg yolk has been found to have better effects on protecting boar spermatozoa against cold shock compared with egg yolk (Jiang et al, 2007).
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