Surface-Bound Sialic Acid on Ram and Bull Spermatozoa: Deposition During Epididymal Transit and Stability During Washing

By use of cytochemistry in conjunction with automatic image analysis it was shown that ram spermatozoa carried a low level of negative charge on, or shortly after, entering the epididymis. The charge increased during passage between the corpus and cauda epididymidis, the increase being caused almost entirely by the addition of sialic acid groups to the sperm surface. After ejaculation, ram spermatozoa retained their net-negative charge, which was again mainly attributable to sialic acid. Ejaculated bull spermatozoa also carried a net-negative charge, about 50% of which was due to sialic acid residues. The sialic acid groups of ejaculated ram and bull spermatozoa were unaffected by a simple but efficient washing procedure, indicating that they were firmly attached to the plasma membrane.