Factors Affecting The In Vitro Maturation Of Buffalo Oocytes

The present study was conducted to investigate factors affecting the in vitro maturation (IVM) of buffalo oocytes. Introduction of thecal cells either in suspension or their conditioned medium (TCCM) to the maturation system resulted in an increase in the proportion of oocytes developing to 2-cell (48.0% and 50.2%) or blastocysts (40.6% and 50.4%) after parthenogenetic activation. When 25% TCCM was added to the maturation medium, significantly more oocytes cleaved (78.3%) and developed to blastocysts (53.4%) after activation in comparison with the control group (55.0% and 38.1%, p<0.05). In addition, the proportion of oocytes matured in TCCM collected from thecal cell cultures on D3 to D4 developing to blastocysts was also significantly higher than that of oocytes matured in TCCM from Dl to D2 and D5 to D6 (62.9% vs 44.1% and 49.3%, p<0.05). Significantly more oocytes extruded the first polar body (PBi) when they were matured in the maturation medium supplemented with 10% estrous cow serum (ECS) compared with 5% and 10% fetal bovine serum (FBS), but no significant difference was found in their proportion cleaved and developing to blastocysts among these groups. However, the cleavage rate (68.3%) and blastocyst yield (44.4%) of oocytes matured in 10% FBS were significantly higher than that of oocytes matured in 10% estrous buffalo serum (BBS) (58.0%, 33.1%; p<0.05), although the proportion of oocytes emitted PBi was significantly lower in 10% FBS (62.7%) than in 10% BBS (74.6%, p<0.05). Addition of 10% BFF (bovine follicle fluid) to the maturation medium resulted in a significant increase in the percentage of oocytes developing to blastocysts (39.6% vs 27.8%, P<0.05), but decreased the proportion of oocytes emitted the first polar body (P<0.05).In conclusions, (1) The introduction of thecal cells either in suspension or conditioned medium to the maturation system may favor the in vitro maturation of buffalo oocytes; (2) The optimum time to collect TCCM is proved to be on D3 to D4 of thecal cell culture and the appropriate proportion of TCCM in maturation medium is 25%; (3) FBS has a positive action on the cytoplasmic maturation of buffalo oocytes, while ECS has a positive action on the nuclear maturation of buffalo oocytes; (4) Follicular fluid can promote the cytoplasmic maturation of buffalo oocytes, but inhibit the nuclear maturation of buffalo oocytes.