Fertilization following mixed insemination with 'cervix-selected' and 'unselected' spermatozoa in the rabbit.

The possible selection of spermatozoa for fertilization by the female genital tract was investigated using genetically homogeneous, numerically adjusted 'cervix-selected' and 'unselected' rabbit spermatozoa. Samples of spermatozoa were marked by 15 min exposure to 1.3 mg TEPA/ml and then washed for 15 min. TEPA-treated and control samples were inseminated alternately into the vagina (= 'cervix-selected') or uterine horns (= 'unselected') of prospective donors. After 6 h spermatozoa were recovered from the uterine horns of the donors. Equal numbers of 'selected' and 'unselected' spermatozoa were inseminated either into the uterine horns (24 does) or oviducts (25 does) of recipients. The fertilization rates were 48 and 72%, respectively. Significantly more eggs were fertilized by untreated than by TEPA-treated spermatozoa. Almost identical fertilization rates, however, were observed between 'cervix-selected' and 'unselected' spermatozoa. It is concluded, therefore, that in the rabbit no selection of (preincubated) spermatozoa for fertilization takes place at the cervical level.