126 INFLUENCE OF PERIPHERAL PROGESTERONE CONCENTRATION ON MORPHOLOGICAL OOCYTE QUALITY IN REPEATED OVUM PICKUP SESSIONS

Abstract

Today, ovum pickup (OPU) followed by in vitro production (IVP) of bovine embryos is an integral part of many breeding programs. The quality of the obtained cumulus–oocyte complexes (COC) limits the success of embryo production. The developmental competence of the COC is dependent on several factors, including the stage of the oestrous cycle, the stage of follicular development and the follicular diameter. The aim of the present study was to determine the influence of circulating progesterone (P4) concentrations during repeated OPU sessions on the morphological quality of bovine COC. Cumulus–oocyte complexes were aspirated twice weekly for 5 to 6 weeks from 12 Holstein Friesian heifers. The first OPU session took place on Day 7 of the oestrous cycle (ovulation = Day 0). During each session, number and diameter of the punctuated follicles and diameter, consistency and cavities in the corpus luteum (CL) were recorded. Follicles were assigned to 3 groups according to their diameter (3 to 5 mm = small follicles; 6 to 8 mm = intermediate follicles; >8 mm = large follicles). Additionally, blood samples were taken at the time of each OPU session and blood P4 concentration was determined using a radioimmunoassay. The COC were categorised as IVP-suitable (round, ≥3 layers of cumulus cells, homo- or heterogeneous ooplasm) or unsuitable according to their morphological quality. All animals showed signs of oestrus accompanied by the presence of large follicles during the course of the OPU sessions. Statistical analysis was performed by an ANOVA followed by a Tukey test. A P-value of <0.05 was considered significant. The mean (±s.e.m.) cycle lengths for all heifers were 23.8 ± 4.6 days. Following the aspiration of a large follicle, a CL-like structure could be detected (referred to as “induced CL”). According to the P4 concentrations, the cycle was divided into 4 phases: natural CL phase (nCL; P4 ≥1 ng mL^–1), follicle phase 1 (Fp1; P4 <1 ng mL^–1), induced CL phase (iCL; P4 ≥1 ng mL^–1), or follicle phase 2 (Fp2; P4 <1 ng mL^–1). During the nCL phase, blood P4 concentrations were significantly higher than during the iCL phase (4.9 ± 2.3 ng mL^–1, n = 12 vs 3.0 ± 1.6 ng mL^–1, n = 10). There were no differences in follicle numbers, the diameter distribution of follicles, recovery rates, or number of retrieved IVP-suitable COC (nCL: 3.1 ± 3.4; Fp1: 3.3 ± 3.7; iCL: 2.7 ± 3.0; Fp2: 3.7 ± 3.7; Table 1). In summary, circulating P4 concentrations had no effect on follicle number, diameter, recovery rate, or IVP suitability of recovered COC.

Table 1.  Number of follicles, retrieved oocytes, follicle sizes and recovery rates of the ovum pickup (OPU) sessions