Contralateral ovarian location between the future ovulatory follicle and extant corpus luteum increases the length of the luteal phase and number of follicular waves in heifers

Location of the future ovulatory follicle and CL in the same ovary (ipsilateral) or opposite ovaries (contralateral) and number of major follicular waves (two or three) per interovulatory interval (IOI) was studied in 14 heifers. Follicle diameter and a blood sample for progesterone (P4) assay were obtained each day throughout an IOI. Heifers were partitioned into three groups: ipsilateral follicle/CL relationship and two follicular waves (Ipsi-2W, N = 5), contralateral relationship and two follicular waves (Contra-2W, N = 5), and contralateral relationship and three waves (Contra-3W, N = 4). Only one heifer had an ipsilateral relationship and three waves and was not included in the analyses. An unexpected observation was slower growth of the dominant follicle of Wave 1 in the Ipsi-2W group than in the Contra-2W and Contra-3W groups. Increased P4 production in the Contra-3W group compared with the Ipsi-2W and Contra-2W groups was indicated by significantly greater P4 concentration averaged over Days 0 to 20 (Day 0 = ovulation), longer interval from ovulation to the beginning of a decrease in P4 and to the beginning of postluteolysis (P4 <1 ng/mL), and longer IOI. The interval from the beginning of postluteolysis to ovulation was not different among groups, indicating that the prolonged IOI reflected the prolonged luteal phase. An effect of the follicle/CL relationship on length of the IOI was not detected in mares. Results supported the hypothesis that the prolonged luteal phase of the contralateral follicle/CL relationship favors the development of three follicular waves/IOI in heifers.