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Follicle and hormone dynamics in single versus double ovulating heifers

¹ Eutheria Foundation, Cross Plains, Wisconsin 53528, USA² Departamento de Zootecnia, Universidade Federal de Viçosa, 36570 Viçosa, Minas Gerais, Brazil³ Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison, 1656 Linden Drive, Madison, Wisconsin 53706, USA

Correspondence should be addressed to O J Ginther at Eutheria Foundation, Department of Pathobiological Sciences, School of Veterinary Medicine, University of Wisconsin-Madison; Email: ginther{at}vetmed.wisc.edu

Follicles 5 mm were ablated at 4 day post-ovulation in heifers to induce a follicular wave, and prostaglandin F₂ was given at day 6 to increase the incidence of double ovulations. Follicle diameters and plasma hormone concentrations were compared between single ovulators (n=12) and double ovulators (n=8). In double ovulators, the interval from follicle deviation to the peak of the pre-ovulatory LH surge was shorter (1.9±0.2 vs 2.5±0.2 days; P<0.02) and diameter of the largest pre-ovulatory follicle was smaller (12.2±0.5 vs 13.3±0.3 mm; P<0.02). The LH concentrations of the pre-ovulatory surge did not differ between single and double ovulators for 24 h on each side of the peak. When data were normalised to LH peak, the peak of the pre-ovulatory FSH and oestradiol (E₂) surges occurred in synchrony with the peak of LH surge for both groups. Concentration of FSH for 24 h on each side of the peak showed a group effect (P<0.0001) from lower concentration in the double ovulators. A group-by-hour interaction (P<0.008) for E₂ reflected greater concentration in the double ovulators before and at the peak. Results indicated that two pre-ovulatory follicles resulted in an earlier and greater E₂ increase, leading to lower FSH concentration, an earlier LH surge, and ovulation at a smaller diameter. In conclusion, the difference in hormone concentrations during the pre-ovulatory period was an effect rather than a cause of double ovulations.