Proteins in stallion seminal plasma

Motility and fertility of frozen-thawed semen differs greatly amongst stallions. Differences in seminal plasma might be one cause of this variation. For 8 ejaculates from each of 17 stallions, seminal plasma was saved at -20 degrees C and spermatozoa were cryopreserved. Based on post-thaw sperm motility, seminal plasma samples from 7 stallions (2 good, 3 variable, 2 poor sperm motility) were selected for measurement of electrolytes, protein content and analysis by sodium dodecylsulphate gel electrophoresis (10% gel, Coomassie blue stain). Variation in seminal plasma was significant (P less than 0.05) amongst stallions for concentrations of Na, K, Ca and Cl, but not for P or protein. A total of 27 proteins, of 13,000 to 122,000 molecular weight, were detected in seminal plasma. There was a difference (P less than 0.05) amongst stallions in the proportion of ejaculates containing 13 of the 27 proteins. However, only for Proteins 23 and 26 was there a significant correlation between the relative amount of protein and sperm motility (0, 30 or 60 min after thawing; r = 0.42-0.50). These correlation coefficients, or those with concentration of K, were too low to be of predictive value. Therefore, although an effect of a minor protein can not be excluded, variation in the relative amounts of major proteins in seminal plasma probably is not a cause of differences in post-thaw motility of stallion spermatozoa.