Influence of seminal plasma on fertility of fresh and frozen-thawed stallion epididymal spermatozoa.

The use of epididymal stallion spermatozoa for routine artificial insemination can secure easy future use of valuable genetics after unforeseen death or injury of a valuable stallion. The aims of this study were to (1) directly compare pregnancy rates for fresh and frozen-thawed stallion epididymal and ejaculated spermatozoa after conventional artificial insemination and (2) to investigate the effect of seminal plasma on the fertility of epididymal spermatozoa after insemination. Twenty-one mares were randomly assigned to three stallions. Mares were inseminated at five consecutive oestrous periods using fresh ejaculated spermatozoa (Fr-E, n=18), fresh epididymal spermatozoa that had been exposed to seminal plasma (Fr-SP+, n=12) or fresh epididymal spermatozoa that had never been exposed to seminal plasma (Fr-SP-, n=9), frozen-thawed ejaculated spermatozoa (Cr-E, n=18), frozen-thawed epididymal spermatozoa that had been exposed to seminal plasma prior to freezing (Cr-SP+, n=18) and frozen-thawed epididymal spermatozoa that had never been exposed to seminal plasma (Cr-SP-, n=15). Pregnancy examinations were performed 14 days after each ovulation. Pregnancy rates were 55.6% (Fr-E, 10/18), 75% (Fr-SP+, 9/12), 22.2% (Fr-SP-, 2/9), 38.9% (Cr-E, 7/18), 27.8% (Cr-SP+, 5/18) and 6.7% (Cr-SP-, 1/15). Overall pregnancy rates for fresh and frozen-thawed epididymal spermatozoa that had been exposed to seminal plasma were significantly better than for epididymal spermatozoa that had never been exposed to seminal plasma (P<0.05). We conclude that the exposure of stallion epididymal spermatozoa to seminal plasma improves pregnancy rates.