Effect of intrauterine threads on fertilization rate in ewes.

Three experiments were conducted using a total of 84 ewes to determine the effects of bilateral or unilateral insertion of intrauterine threads on fertilization rate and unilateral insertion on embryonic survival. In experiment I bilateral insertion of intrauterine threads significantly reduced the proportion of ewes with fertilized ova 3 days after mating. Intrauterine threads inhibited fertilization without shortening the lengths of estrous cycles immediately prior to mating. In experiment 11 the presence of an intrauterine thread ipsilatcral, but not contralateral, to the side of ovulation significantly reduced the proportion of ewes with fertilized ova 3 days after mating. Twelve days after mating (experiment I11) the pregnancy rate of ewes ovulating on the ovary ipsilateral to the intrauterine thread was approximately one-half that of the ewes in sham operated or contralateral groups. The results of these experiments indicate that the major antifertiiity effect of intrauterine threads in ewes is an inhibition of fertilization when ovulation occurs ipsilateral to a uterine horn containing the thread. The experiments failed to provide evidence that the intrauterine threads modify the uterine environment in a manner that would cause early embryonic mortality. (