In vitro fertilizing ability of testicular, epididymal, and ejaculated rabbit spermatozoa

The fertilizing ability of testicular, epididymal, and ejaculated rabbit spermatozoa was evaluated in vitro following in vitro capacitation by high ionic strength treatment. Fewer than 11% of inseminated ova were apparently fertilized (i.e., in pronuclear, two-, and four-cell stages as determined by light microscopy) when testicular sperm treated with caffeine, caput epididymal, or corpus epididymal sperm samples were tested. A greater fertilizing ability, reflected by the percentage of ova fertilized and more normal progression of embryonic development, was exhibited by cauda epididymal sperm. Of 93 ova, 68 (73.1%) were fertilized by cauda sperm, whereas ejaculated sperm from the same 10 bucks fertilized 34 (36.6%) of 93 ova (P is less than 0.005). Ultrastructural examination of selected ova apparently fertilized by sperm from levels of the male reproductive tract proximal to the cauda epididymidis revealed abnormal activation. Authentic fertilization occurred when ova were inseminated with cauda epididymal and ejaculated sperm. An unusual and infrequent form of activation involving failure of cortical granule breakdown in ova penetrated by cauda epididymal and ejaculated sperm was seen. A comparison of fertilizing ability of sperm from first, second, and third ejaculates revealed a significant decrease with the third ejaculate (P is less than 0.01).