Interestrous intervals in cows after unilateral ovariectomy at estrus to prevent corpus luteum development

Abstract

Two experiments were conducted to answer the question: What happens to the estrous cyclicity pattern of cows if ovulation and subsequent corpus luteum (CL) development are prevented by removing the ovary containing the largest follicle during estrus? In Experiment 1, the mean interestrous interval of the first estrous cycle after this procedure was 5.6 ± 0.6 days for 10 cows (one outlier of 2.5 d and one cow that ovulated from the remaining ovary were excluded) versus a 21.0 day mean for control cycles in the same cows. In Experiment 2, the same unilateral ovariectomy procedure was done but the effect of its timing was tested by performing the procedure before (n = 7 cows) or after (n = 5 cows) the anticipated luteinizing hormone (LH) surge at a prostaglandin-controlled estrus. Intervals to estrus (6.1 vs. 5.8 d) or to its LH surge (5.8 vs. 5.8 d) did not differ between these groups. Two cows treated before the LH surge that developed follicular cysts and one cow treated after the LH surge that ovulated from the remaining ovary were excluded. Therefore, the time required for cows to return to estrus from this controlled baseline point (unilateral ovariectomy at estrus of the ovary with the ovulatory follicle) was highly predictable (5.8 ± 0.6, n = 19), and the ovulatory mechanism, including magnitude of the LH surge, recovered in most cows despite the short interestrous interval.