207 DEVELOPMENT OF A ROUTINE IN VITRO EMBRYO PRODUCTION SYSTEM USING SINGLY IN VITRO-MATURED, FERTILIZED, AND CULTURED BOVINE OOCYTES

Abstract

An in vitro embryo production system (IVP), in which a single oocyte can be tracked from the moment of retrieval up to the blastocyst stage, would be a valuable tool for studies linking developmental competence and embryo metabolism to oocyte quality and follicular environment. Unfortunately, to date, data on individual IVP are inconsistent, and in most cases show unsatisfactory blastocyst rates. Earlier studies revealed that individual culture on a cumulus cell (CC) monolayer resulted in comparable numbers of good-quality embryos as obtained after regular group culture (Goovaerts et al. 2008 Reprod. Dom. Anim. 43 (Suppl. 3), 190). Because, in the latter study, single culture was performed after group maturation and fertilization, the aim of this study was to develop and test an individual IVP system using bovine oocytes or zygotes obtained after single maturation and single fertilization. Therefore, 532 grade I COC from slaughterhouse ovaries (3 replicates) were randomly assigned to 1 of 2 treatments: a complete individual IVP protocol, or a routine group IVP as a control. Individual maturation (TCM-199 + 20% serum) and fertilization were performed in 20-μL droplets under oil in 24-well plates. Subsequently, each zygote was cultured in 20 μL of medium (SOF + 5% serum, 90% N₂, 5% CO₂, 5% O₂) on a 6-day-old monolayer of matured CC (5% CO₂ in air). Group maturation and fertilization were carried out per 100 COC in 500 μL, whereas group culture was performed per 25 zygotes in 50-μL droplets under oil. Cleavage, blastocyst, and hatching rates were assessed 2, 8, and 10 days postfertilization, respectively. Possible effects of individual and group culture were evaluated with binary logistic regression (SPSS 15.0). No interactions between replicate and treatment could be found (P > 0.05). Cleavage and blastocyst rates were significantly lower after individual IVP, compared with group IVP, whereas the blastocyst rates on cleaved zygotes and the hatching rates did not differ significantly (Table 1). In conclusion, acceptable blastocyst rates (25.1%) could be obtained after individual IVP. The lower blastocyst rates were associated with the lower cleavage rates, and no effect of the individual embryo culture system on embryo development could be found.

Table 1.  Cleavage, blastocyst, and hatching rates after individual and group in vitro embryo production (IVP)