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

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.