Dilauroylphosphatidylcholine liposome effects on the acrosome reaction and in vitro penetration of zona‐free hamster eggs by bull sperm: I. A fertility assay for fresh semen

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Abstract
Fresh sperm from five bulls having nonreturn rates ranging from 48% to 77% were treated with 15.7, 21.0, 26.2, 31.5, 36.7, and 42.0 μM dilauroylphosphatidylcholine (PC12) to induce the sperm acrosome reaction (AR). Treated sperm were incubated 3 hr with zona‐free hamster eggs at 39°C prior to fixation. The eggs were then stained and examined for sperm penetration. Differences in the percentages of motile sperm and of sperm exhibiting an AR among bulls were small when compared on a within‐liposome‐concentration basis. Increasing the PC12 concentration from 15.7 μM to 42.0 μM increased the percentage of sperm exhibiting an AR for all bulls. At the lowest lipid concentration (15.7 μM), the percentage of eggs penetrated by sperm from the five bulls was 6% to 36%, with 0% in controls. When sperm were incubated with increasing lipid concentrations, the egg penetration rate increased to over 80%, and the total number of sperm increased to over 100 per 36 eggs in each treatment for every bull. These penetration rates decreased at the highest lipid concentration. A correlation between the PC12 concentration maximizing egg penetration and the nonreturn rate of −.63 was found. The correlation between the PC12 concentration maximizing the total number of penetrated sperm per treatment and the bull nonreturn rate was −.96. It was concluded that PC 12 liposomes induce the AR in bull spermatozoa, which enables them to penetrate zona‐free hamster eggs. High fertility bulls required less lipid to induce the AR than did lower fertility bulls. Consequently, this assay of fresh semen could provide a laboratory method to estimate the fertility of a bull.