Effects of Day of Insertion of Intrauterine Devices on Luteal Function in Ewes

Large spiral intrauterine devices (IUDs) were inserted into both uterine horns of at least four ewes on each day of the estrous cycle. Ewes which had IUDs inserted on or before Day 3 usually had markedly shortened insertion cycles and the luteal phase (measured by peripheral progesterone concentration) was absent. In contrast, when the devices were inserted after Day 3, cycle length and luteal function were normal or prolonged. In some ewes, there was an extended period between the end of luteal function and the exhibition of estrus. The luteolytic action of IUDs inserted early in the cycle was inhibited by intravaginal sponges contained in medroxyprogesterone acetate.