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

The time of uterine involution and the changes in ovarian follicle populations were studied during early postpartum in multiparous, suckling Corriedale ewes lambing in the autumn. On Day 1 (n=5), Day 5 (n=4), Day 17 (n=4) and Day 30 (n=3) postpartum ewes underwent surgery to obtain ovaries and uteri. The weights of uteri and the lengths of the previous pregnant and nonpregnant horns were recorded as well as the presence 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) during the first 17 days and then remained constant. When uterine parameters from uteri obtained at Days 17 and 30 were compared with those of 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 medium (> 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 ewes macroscopic uterine involution was complete around Day 17 post partum and that follicle development begins immediately after parturition, reaching preovulatory size before Day 17. In 2 of the 3 ewes studied until Day 30, ovulation (first progesterone increase) occurred after Day 17 (Days 18 and 25).