Superovulation following follicular synchronization with GnRH at random stages of the oestrous cycle in heifers: oocyte competence and in vitro embryo production

The objective of this study was to develop a superovulatory program based on the synchronization of follicular waves with GnRH which could be applied regardless of the stage of the oestrous cycle. In this experiment, GnRH was given to 30 heifers in lactation between Days 0 and 7 (n = 13), 8 and 12 (n = 12), 13 and 16 (n = 5) of the oestrous cycle. Twenty-four heifers were used as controls and did not receive any GnRH. All follicles ≥ 6 mm were punctured 4 days after GnRH treatment in treated animals and between Days 8 and 12 of the oestrous cycle in control heifers. Two days after the follicular puncture, all heifers were superstimulated with 160 mg Folltropin-V given twice daily over 2 days. Oocytes were collected 42 h after the last FSH treatment. The oocytes were subjected to IVM/IVF and the developmental competence of embryos was compared. In vitro production of embryos was affected only by the stages of the oestrous cycle when the GnRH treatment was given and not by the GnRH treatment. No difference (P > 0.1) in the mean number of oocytes, cleavage and embryo production was noted between the control animals and the animals treated with GnRH in the late phase of the oestrous cycle. The mean number of blastocysts was higher (P < 0.05) in heifers treated with GnRH in the mid and the late phase of the oestrous cycle than in the early phase. In conclusion, the in vitro production of embryos was compromised in the present study with heifers following the follicular synchronization with GnRH. This procedure is advantageous for the in vitro production of bovine embryos since the spontaneous oestrus is eliminated. However, more investigations are needed to increase the competence of oocytes obtained following this procedure.