Ovarian Follicular Changes Following Unilateral Ovariectomy in the Cow1

Twenty-four Holstein heifers were used in a 2 × 2 factorial experiment to study the effect of unilateral ovariectomy, performed on day 8 of the estrous cycle, upon cycle length and upon follicle number and size in the retained ovary at the next estrus. The factors were the number of ovaries (one or two) and the presence or absence of the corpus lutem (CL) in each animal. In the presence of the CL, the one-ovary and the intact animals did not differ significantly in cycle length (21.2 and 20.0 days, respectively); in the absence of the CL, the one-ovary heifers had a significantly longer cycle length (13.2 days) than the intact heifers (10.2 days). The number of follicles 5 mm or more in diameter was significantly greater in the retained ovary of the one-ovary animals than in the corresponding ovary of the intact animals; total follicular fluid, however, was practically equal in both groups. The largest follicle in the retained ovary of the one-ovary animals was smaller than the largest follicle in either ovary of the intact animals. The total follicular surface area in the retained ovary of the one-ovary animals was almost twice as large as that of the corresponding ovary of the intact animals. These results demonstrate ovarian compensatory changes (in the presence or absence of the CL) following unilateral ovariectomy in a monotocous species.