Protein and lipid species in seminal plasma of fertile Holstein-Friesian bulls

Abstract

Protein and lipid molecules in seminal plasma (SP) collected from fertile bulls were investigated. Semen was collected from 10 bulls (2 ejaculates each) and examined for standard semen analysis. Raw SP was recovered by centrifugation and total protein (TP) concentration was determined using a refractometer. Raw SP was desalted using a Sephadex G-25 desalting column then both raw and desalted SP was subjected to SDS-PAGE. Neutral lipids and phospholipids of raw and desalted SP were separated by thin-layer chromatography (TLC). The results revealed that, all bulls had normal semen characteristics and TP concentration in SP ranged from 7.0 to 10.4 g/dL except bull No. 6 had a relatively low concentration of 4.9 to 6.8 g/dL. Neither proteins nor lipids species were different between raw and desalted SP. Seventeen proteins were detected ranging from 8.5 to 185.8 kDa, and those of 12, 13.5, 15, 21, 23 and 38 kDa were predominant. Notably, proteins of 10, 17.5, 19, 21, 80 and 185.8 kDa might be new candidates of SP proteins (SPPs). The detected neutral lipid spots corresponded to cholesterol, 1,2-dimyristoyl glycerol, 1,2-dioleoyloglycerol, 1,3-dimyristoyl glycerol and 1,3-dioleoyloglycerol. The detected phospholipids spots corresponded to non-migrating phospholipids, sphingomyelin (SM), phosphatidylcholine (PC), phosphatidylserine (PS), phosphatidylinositol (PI), phosphatidylethanolamine (PE), cerebroside and polyglycerol phosphatide. Cholesterol represents the major molecule of neutral lipids, whereas SM, PC, PI and PE represent the major phospholipids. Noteworthy, there were 2 species of diacylglycerol (DAG) and 3 species of PI in bovine SP. In conclusion, this study gave a general picture of SP protein and lipid species in fertile bull semen, which might serve as fundamental knowledge for either semen analysis or prediction of male fertility.