UTERINE INVOLUTION AND OVARIAN CHANGES DURING EARLY POSTPARTUM IN AUTUMN-LAMBING CORRIEDALE EWES

The time of uterine involution and the changes in ovarian follicle pop ulations were studied during early postpartum in multiparous, suckling Corriedale ewes lambing in the autumn. On Day 1 (n=5), Day 5 (n=4), D ay 17 (n=4) and Day 30 (n=3) postpartum ewes underwent surgery to obta in ovaries and uteri. The weights of uteri and the lengths of the prev ious pregnant and nonpregnant horns were recorded as well as the prese nce of ovarian follicles larger than 1 mm in diameter. Uterine weight and length of uterine horns decreased (P less-than-or-equal-to 0.01) d uring the first 17 days and then remained constant. When uterine param eters from uteri obtained at Days 17 and 30 were compared with those o f 6 cyclic ewes, no differences were found. On Day 1 only small (1 to 2 mm) follicles were observed on the ovarian surface, while on Day 5 m edium (> 2 to < 4 mm) follicles were also present. At days 17 and 30, aside from the small and medium follicles, all the ewes also had large (greater-than-or-equal-to 4 mm) follicles, and, at Day 30 2 ewes had large corpora lutea. We conclude that in autumn-lambing Corriedale ewe s macroscopic uterine involution was complete around Day 17 post partu m and that follicle development begins immediately after parturition, reaching preovulatory size before Day 17. In 2 of the 3 ewes studied u ntil Day 30, ovulation (first progesterone increase) occurred after Da y 17 (Days 18 and 25).