In vitro maturation and fertilization, and subsequent development of buffalo (Bubalus bubalis) embryos: effects of oocyte quality and type of serum

Abstract

In Experiment 1, to determine the developmental potential of buffalo oocytes of different qualities, compact cumulus–oocyte complexes (COCs) with an unexpanded cumulus mass, and with homogeneous ooplasm were classified as Grade 1 (with 5 layers of cumulus cells) and Grade 2 less than 4 layers of cumulus cells). Grade-3 oocytes were either without cumulus cells or with expanded cumulus mass, and with irregular ooplasm. The oocytes were matured for 24 h at 38·5°C, 5% CO₂ in air in maturation medium (10% fetal bovine serum (FBS) in TCM-199 supplemented with 5 µg mL^-1 follicle stimulating hormone-P). The nuclear maturation and cleavage rates, and the proportion of cleaved embryos which developed to morula and blastocyst stage were in the order Grade 1>Grade 2>Grade 3 (P < 0·05). For Experiment 2, the maturation medium consisted of TCM-199 supplemented with one of the following sera at 10% concentration: (1) buffalo oestrus serum (BOS), (2) superovulated buffalo serum (SBS), (3) fetal bovine serum (FBS) and (4) steer serum (SS). After in vitro fertilization (IVF), the oocytes were co-cultured with buffalo oviductal epithelial cells in TCM-199 containing the respective sera at 10% concentration for the subsequent 9 days. The extent of cumulus expansion and nuclear maturation were not different among different groups. The cleavage rates were lower (P < 0·05) with FBS than with BOS, SBS and SS. The proportion of cleaved embryos which developed to blastocyst stage was higher (P < 0·05) with SBS than with BOS, FBS and SS.