Bovine serum albumin, sperm motility, and the "dilution effect'

Epididymal spermatozoa from rabbit and ram were washed either once or twice using an efficient washing procedure and were then diluted in various media to a final concentration of approximately 1.4 x 10(7) cells/ml and incubated at 30 degrees C for up to 12 hours. Bovine serum albumin (BSA), either untreated or defatted, was found to be better than polyvinylpyrrolidone, ovalbumin, or alpha-lactalbumin, both at stimulating and maintaining motility levels and at reducing the tendency of the washed spermatozoa to stick to glass. BSA was effective in all media tested, being independent of Ca2+, PO4(3-), HCO3-, and ionic strength). BSA has a reversible stimulatory effect on motility. If BSA was added to sperm suspensions 3 1/2 hours after they had been washed and diluted in protein-free medium, motility was stimulated to levels not significantly lower than those observed in samples that had been washed and diluted in the presence of BSA. However, samples washed into BSA and then washed free of it behaved essentially as though they had never been in contact with protein. The motility, survival, and response to BSA of twice-washed spermatozoa were the same as those of once-washed spermatozoa, showing that epididymal plasma factors are not required for survival in vitro. It was concluded that dilution is not essentially detrimental to rabbit and ram spermatozoa. However, severe dilution of semen may result in levels of male reproductive tract fluids insufficient either to stimulate motility or to prevent sticking of motile cells to container surfaces. Few motile spermatozoa are recovered from samples of such diluted semen.