Conversion of intraovarian patterns from preovulation to postovulation based on location of dominant follicle and corpus luteum in heifers

Abstract

The conversion of preovulatory intraovarian patterns based on location of the preovulatory follicle (PF) and the associated corpus luteum (cl) to postovulatory patterns based on location of the future and established dominant follicle (DF) and corpus luteum (CL) was studied daily in 26 heifers from Days −5 to 6 (Day 0 = ovulation). The two ipsilateral preovulatory patterns were PF–cl and devoid (neither PF nor cl), and the two contralateral patterns were PF and cl. The postovulatory patterns were DF–CL, devoid, DF, and CL. For the contralateral preovulatory relationships, a conversion from PF to DF–CL and the accompanying conversion from cl to devoid occurred most frequently (17 of 18 conversions, 94%). For the ipsilateral preovulatory relationships, a conversion from PF–cl to CL and from devoid to DF occurred most frequently (6 of 8, 75%). Number of 2-mm follicles during preovulation was greatest (P < 0.05) for the devoid and PF patterns, and number of 6-mm follicles during postovulation was greatest (P < 0.05) for the DF–CL and DF patterns. Blood flow resistance at a color Doppler signal in the ovarian pedicle indicated increasing ovarian perfusion over days in the PF to DF–CL and devoid to DF conversions and decreasing perfusion in the PF–cl to CL and cl to devoid conversions. In addition to formation of the CL from the PF, it was interpreted that the conversion of patterns involved number of newly emerging 2-mm follicles per ovary before ovulation and a continuation of the preovulatory angioarchitecture into postovulation. Results supported the novel hypothesis that the four preovulatory intraovarian patterns determine the frequency of the four postovulatory patterns.