176 Synchronisation of follicle wave emergence prior to superstimulation with purified FSH for ovum pickup affects blastocyst rate in pregnant Holstein heifers

The timing of initiation of superstimulatory treatments relative to follicle wave emergence has been shown to affect ovulatory response and invivo embryo production. The significant increase of invitro embryo production (IVP) and the possibility of using pregnant animals as oocyte donors has created the need to optimise superstimulatory treatments for IVP in pregnant cattle. Thus, the objective of the present study was to evaluate the effect of synchronisation of follicle wave emergence before superstimulation for ovum pickup (OPU) and IVP in pregnant heifers. Pregnant (47-62 days of gestation) Holstein heifers (n=28) 19.5±0.3 months of age were assigned in a completely randomised design to one of two groups: synchronisation of follicular wave emergence by dominant follicle removal (DFR; all follicles >6mm) or untreated control (no DFR). Superstimulatory treatments were initiated 36h after DFR or at random stages of the follicular wave in the no-DFR group and consisted of the administration of 160mg of purified FSH (Folltropin-V, Vetoquinol) over four injections 12h apart as follows: 48.0, 42.7, 37.3, and 32.0mg. Ovum pickup was performed in all heifers 40h after the last purified FSH injection. Heifers were subjected to OPU for oocyte recovery, and the number of follicles was determined. Recovered oocytes were processed in groups by treatment, and IVP was performed. Differences between treatment groups were evaluated using generalised linear mixed models. Results are presented in Table 1 and are expressed as means±s.e.m. for data collected at the time of OPU or as proportions for embryo production results. The number of small follicles (<6mm) at the time of OPU was greater in the no-DFR group than in the DFR group (P=0.04). Conversely, there were no differences between treatments in the number of medium follicles (6-10 mm; P=0.17), large follicles (>10 mm; P=0.11), total follicles (P=0.93), total number of recovered oocytes (P=0.4), or number of viable oocytes (P=0.53). The mean oocyte percentage recovery rate was not different between heifers in the DFR (53.6±4.7%) and no-DFR (56.5±4.7%) groups (P=0.52). Both cleavage and blastocyst rate were greater (P<0.008) in the DFR group than in the no-DFR group; as a result, the number of transferable embryos per animal was 5.6 in the DFR group and 2.8 in the no-DFR group. In summary, initiation of superstimulatory treatments at the time of follicle wave emergence improves cleavage and blastocyst rates, thus leading to greater embryo production. Table 1.Ovarian response and embryo production in pregnant heifers superstimulated with or without synchronisation of follicle wave emergence Variable DFR No DFR Small follicles, n 8.1±1.2A 12.1±1.8B Medium follicles, n 18.3±1.3 13.7±2.0 Large follicles, n 2.4±0.6 1.4±0.4 Total follicles, n 28.8±1.4 27.2±2.2 Total oocytes, n 15.4±1.5 16.0±1.9 Viable oocytes, n 13.7±1.5 13.4±1.8 Cleavage rate,% (n) 77.1 (192)A 64.4 (188)B Blastocyst rate,% (n) 40.6 (192)A 20.7 (188)B A,BMeans within a row with different superscripts differ (P<0.05).