AbstractCycling rats were hysterectomized and/or unilaterally ovariectomized (ULO) on day 2 (metestrus). Collateral blood supply to the remaining ovary via the uterine artery was left intact or disrupted. Animals were killed in metestrus after one complete estrous cycle. Control rats were also killed at this time.Counts of tubal ova revealed that intact rats ovulated an average of 4.4 ± 0.4 eggs per ovary (N = 8). Following ULO, rats (N = 8) ovulated 9.6 ± 0.2 eggs. Ligation of the uterine artery decreased the number of eggs ovulated in ULO rats (N = 8) to 5.4 ± 1.1. Hysterectomized rats (N = 8) ovulated 4.8 ± 0.5 eggs per ovary. If the blood supply was disrupted, a reduction to 2.7 ± 0.2 eggs per ovary occurred (N = 8). Hysterectomized and ULO rats (N = 8) ovulated 10.3 ± 0.4 eggs from the remaining ovary but only 5.0 ± 1.0 eggs if the collateral blood supply of the uterine artery was not intact (N = 10).The results demonstrate that disruption of the vascular channels during the surgical procedures of hysterectomy and/or ULO results in a reduction of the expected ovulation