Uterine contraction patterns and fertility in early postpartum ewes

Three experiments were conducted to determine: (1) the direction of uterine contractions in Days 32 and 52 postpartum ewes (Experiment 1); (2) the effect of PGF(2alpha) on direction of uterine contractions (Experiment 2); and (3) the effect of PGF(2alpha) on fertility rates in Day 32 postpartum ewes (Experiment 3). In Experiment 1, non-lambing (>90 days postpartum) and lambing ewes (day of lambing=Day 0) received medroxyprogesterone acetate (MAP) vaginal sponges for 8 days and 500 IU of eCG at sponge withdrawal (Days 30 or 50 postpartum). At the time of eCG injection, ewes were divided into the following groups: (1) non-lambing (control; n=29); (2) Day 32 postpartum dry (n=15) and lactating (n=16); and (3) Day 52 postpartum dry (n=14) and lactating (n=16). At estrus or 60h post-eCG, the uterus was exteriorized through a mid-ventral incision, and the origin and direction of uterine contractions were recorded for 10min. In Experiment 2, ewes received MAP sponges on Day 16 postpartum followed by 500 IU of eCG on day of sponge removal (Day 30). At estrus, the ewes were divided into the following treatments: (1) two injections of saline 4h apart (n=10) and (2) 12.5mg of PGF(2alpha) followed by another 12.5mg 4h later (n=7). After the second injection, ewes were laparotomized and uterine contractions were counted. In Experiment 3, estrus was induced in postpartum ewes, and ewes were mated to two rams, then received the same two treatments as described in Experiment 2 (ram+saline; n=32 and ram+PGF(2alpha); n=28). Two days following mating, ewes were laparotomized and the oviducts flushed for recovery of ova. In Experiment 1, lactational status had no effect, therefore, the data were pooled. Control ewes had a greater percentage (p<0.05) of uterine contractions (69%) moving towards the oviducts than did Day 32 (8%) or Day 52 (43%) ewes. In Experiment 2, PGF(2alpha) treatment increased the proportion of contractions (p<0.05) moving toward the oviducts (controls 16%, PGF(2alpha) 42%). Number of PGF(2alpha)-treated ewes (Experiment 3) with fertilized ova were not significantly different from the control ewes (5/32 versus 2/28; respectively). In conclusion, it can be said that the direction of uterine contractions moving toward the oviducts increased as the postpartum interval progressed or if they received PGF(2alpha) injection. PGF(2alpha) treatment did not improve fertility rates in Day 32 postpartum ewes.