Effects of follicular fluid supplementation of in-vitro maturation medium on the fertilization and development of equine oocytes after in- vitro fertilization or intracytoplasmic sperm injection

The aim of this study was to compare the effect of the addition offollicular fluid (FF) collected from preovulatory follicles with that ofoestrous mare serum (EMS) (acting as the control) to TCM-199 medium on thein-vitro maturation, fertilization and development of equinecumulus-enclosed oocytes. Oocytes (<30 mm in diameter) were obtainedfrom the ovaries of slaughtered mares. After in-vitro maturation in thepresence of the two supplements, their fertilization, cleavage anddevelopmental potential were compared after conventional in-vitrofertilization (IVF) or intracytoplasmic sperm injection (ICSI) usingfrozen-thawed spermatozoa. Follicular fluid did not increase the maturationof oocytes to metaphase II stage compared to control. After IVF, there wasno difference in fertilization rates between FF- supplemented oocytes andcontrols (7/87, 8.4% of oocytes showing two pronuclei with FF versus 7/116,6% with EMS; not significant). However, after ICSI, FF-supplemented oocytesshowed significantly increased normal fertilization (32/85, 37.6% oftwo-pronuclear oocytes) and developmental potential (15/31, 48% cleavage)compared to the control oocytes (7/47, 14.9%, P < 0.01; and 2/48, 4%, P< 0.01, respectively). Overall, ICSI resulted in increased fertilizationrates compared to IVF, regardless of the presence or absence of FF (39/132,29.5% with ICSI versus 14/203, 6.9%). These results suggest that follicularfluid supplementation may improve the maturity of equine cumulus-enclosedoocytes sufficiently for the successful use of ICSI, but not sufficientlyfor normal sperm-egg interaction occurring during IVF.