Effect of number of 6-mm predeviation follicles and intraovarian patterns on right-side ovulation in heifers

Abstract

The mechanisms underlying the greater frequency of ovulation from right ovary (RO) than left ovary (LO) were studied in 145 Bos taurus heifers. Diameter deviation during a follicular wave is indicated by continued diameter increase in the future preovulatory follicle (PF) and a decrease in diameter of future subordinate follicles. The PF (ovulation) was in the RO (63/105, 60%) more frequently (P < 0.04) than in the LO (40%) for ovulatory wave 2 of two-wave interovulatory interval (IOI) but not for wave 3 of three-wave IOI (RO, 45%; LO, 55%). The difference between waves 2 and 3 was associated with a greater (P < 0.01) number of 6-mm follicles during predeviation in the RO (2.3 ± 0.2 follicles) than LO (1.8 ± 0.1) for wave 2 but not for wave 3. Combined for ovulatory waves 2 and 3, the PF developed in the ovary with more 6-mm follicles during more (P < 0.0001) ovulatory waves (72%) than when the PF developed in the ovary with fewer follicles (11%). Ovulation from RO was more frequent (P < 0.02) when both PF and CL were in RO (46/72, 64%) than in LO (36%), but not when PF was alone in RO without the CL. Results supported the hypotheses that: (1) the number of 6-mm predeviation follicles developing during the ovulatory wave is greater for RO and (2) the number of predeviation follicles is greater for the ovary in which the preovulatory follicle subsequently develops.