Progesterone concentration when the future ovulatory follicle and corpus luteum are located in ipsilateral or contralateral ovaries in heifers

Three studies were done on the effects of ipsilateral location (same ovary) versus contralateral location (opposite ovaries) of the future ovulatory follicle and CL in heifers. The numbers of heifers for the ipsilateral and contralateral groups, respectively, were: experiment (Exp) 1 (N = 4 and 4), Exp 2 (N = 6 and 4), and Exp 3 (N = 5 and 10). In the Exps with available data (Exp 2 and 3), the interval between ovulation and the end of luteolysis was significantly shorter in the ipsilateral group than in the contralateral group (Exp 2: 16.8 ± 0.3 vs. 19.8 ± 1.7 days; Exp 3: 16.9 ± 0.2 vs. 19.7 ± 0.9 days). In Exp 3, the interovulatory interval was shorter (P < 0.01) in the ipsilateral group (20.1 ± 0.4 days) than in the contralateral group (22.7 ± 0.7 days), but the interval from the end of luteolysis to ovulation was not altered significantly. Circulating progesterone (P4) concentration for 33 hours normalized to the beginning of luteolysis (Exp 1) and on Days 16 to 20 (Day 0 = ovulation; Exp 3) was significantly lower in the ipsilateral group than in the contralateral group (Exp 1: 3.7 ± 0.2 vs. 4.8 ± 0.3 ng/mL; Exp 3: 1.7 ± 0.4 vs. 5.9 ± 0.4 ng/mL). Area (cm2) of the CL and percentage of CL with color Doppler signals of blood flow were lower and resistance index for a CL arteriole was greater in the ipsilateral group (Exp 3). The decreased P4 concentration in the ipsilateral group began by Day 16, but the decreased luteal area and vascular perfusion were not detected until Days 17 or 18. Results supported the hypothesis that the ipsilateral location of the future ovulatory follicle and CL was associated with lower P4 production and a shorter interovulatory interval.