285 VARIATION FACTORS INFLUENCING CLEAVAGE AND EMBRYONIC DEVELOPMENT RATES OF BOVINE OOCYTES COLLECTED ON A FARM IN A COMMERCIAL OPU-IVP SYSTEM

Abstract

The aim of this work was to identify factors influencing the success rate of each production step through a retrospective study conducted for 362 commercial OPU-IVP sessions performed on a farm. Donor females were stimulated with FSH in five decreasing doses (400 μg for cows and 250 μg for heifers). Collected oocytes were matured for 24 h in M199 plus fetal calf serum, FSH, epidermal growth factor (EGF), and estradiol. They were then fertilized in TALP with frozen-thawed semen; zygotes were cultured for 6 days on Vero cell monolayers in B2 medium. Embryos were transferred as fresh to recipients on Day 7. The effects of donor characteristics, OPU and IVP conditions on cleavage, development rates, and number of transferred embryos (TE) were analyzed by ANOVA (GLM program in SAS; SAS Institute, Inc., Cary, NC, USA). Effects are mentioned when significant at P < 0.05. The mean number of collected oocytes per session was 14; 11.6 were selected for IVM, 8.5 cleaved, and 3.9 developed to the blastocyst stage (40.4% of the embryos were Grade 1, 35.3% G2, and 20.5% G3). On average, 2.9 embryos were transferred into recipients. The number of transferred embryos was higher when the dominant follicle (DF) was punctureed prior to OPU (see Table 1). This resulted in a better cleavage rate in punctured DF donor females. Higher cleavage rates were observed in infertile females as well as numbers of TE per session. Pregnancy and body condition score (BCS) recorded at OPU only influenced cleavage rates. Embryonic development rates were mainly influenced by donor breed and parity. In the Abundance breed, 87.5% of the sessions resulted in at least one embryo being transferred compared to 58.6% in Holsteins. Higher numbers of embryos were transferred per session when donor females were cows rather than heifers. Fertilization conditions (heparin and sperm concentrations) had no effect on cleavage and embryonic development rates. To conclude, cleavage and development rates were mainly influenced by donor characteristics (breed, parity, physiological status). Improvement of results may be achieved by systematic puncture of DF prior to OPU. Cleavage rates were dependent on BCS. To improve management of body condition, BCS variations before OPU could be a new parameter to be followed in donor females.

Table 1. Factors affecting steps of the OPU-IVP procedure