EFFECTS OF S M A L L D I A M E T E R lUDs ON F E R T I L I T Y A N D LENGTHS OF ESTROUS CYCLES IN EWES

Two experiments were conducted utilizing ewes to determine the effects of small diameter IUDs on fertility, lengths of estrous cycles and uterine histology. In both experiments, IUDs were inserted bilaterally at day 3 of the estrous cycle (estrus = day 0). The IUDs were single strands of nylon suture (.3 mm diameter) lying free in the uterine lumen except at a point of attachment near the uterotubal junction. In both experiments, the lengths of the first estrous cycle (cycle in which surgery was performed) and second estrous cycle were determined. All ewes were mated to fertile rams at the estrus beginning the third cycle. In experiment I, ewes which failed to conceive at the first mating were bred to fertile rams at the fourth estrus (no pregnancies occurred), again at the fifth estrus and necropsied 2 or 3 days later. In experiment II, ewes were necropsied 12 days after the first mating with fertile rams. The results-of analysis of variance of the lengths of esff0us cycles for experiments 1 and II showed no significant differences between sham-operated and IUD-treated ewes. Of the 18 sham-operated ewes in experiments I and If, 17 conceived at the first mating with fertile rams. For all 18 IUD-treated ewes in experiments I and II, only one pregnancy resulted from the first mating. The proportion of ewes which became pregnant at the first mating was lower (P<~.01 and P<.05 for experiments I and II, respectively) in the IUD-treated groups than in