Oocyte competence in repeat-breeder heifers: effects of an optimized ovum pick-up schedule on expression of oestrus, follicular development and fertility

Repeat-breeder heifers (RBH) have been shown to present reproductive perturbations during spontaneous cyclicity, which affects oestrus and ovulation. Some of these disturbances ( e. g. deviating hormone patterns) are also present during and after cycles of twice-weekly ovum pick-up (OPU), performed according to an optimized schedule allowing normal oestrous cyclicity. In the present study, the effects of OPU on oocyte competence in in vitro maturation (IVM) and in vitro fertilization (IVF) have been evaluated, as were the effects on expression of oestrus and fertility in five RBH (greater than or equal to 4 artificial inseminations) and five virgin heifers (VH controls). In total, 269 RBH and 174 VH oocytes were scored for quality prior to IVM and IVF. The number of follicles available for puncture was higher in RBH, but the oocyte recovery rate after OPU was lower in RBH compared with VH controls and the recovered RBH oocytes were of lower quality, as judged by their appearance at retrieval. Confocal laser scanning and transmission electron microscopy of immature oocytes did not reveal any differences between RBH and VH control oocytes with respect to nuclear and mitochondrial status. However, after IVM, the cytoplasmic spatial reorganization of mitochondria and cortical granules was less advanced in RBH, which could contribute to the subfertility that defines the syndrome. Cleavage rates after IVF were similar in RBH and VH controls. Subsequent to the OPU period, in vivo fertility after controlled artificial insemination was comparable with field fertility rates in both RBH and VH.