A Preliminary Study On The In Vitro Fertilization (IVF) Of Sheep Oocytes Matured In Vitro

The present study was conducted to investigate factors affecting the in vitro fertilization of sheep oocytes matured in vitro so as to establish a preliminary IVF procedure for sheep. Follicle cutting harvested significantly more usable cumulus-oocytes complexes (COCs) (3.95/ovary) in comparison with follicle aspiration (1.96/ovary, P<0.05) from surface-visible follicles of slaughtered ovine ovaries. After maturation in vitro for 23-25 h, oocytes were fertilized with frozen-thawed ovine sperm in the SOF supplemented with or without estrous sheep serum (ESS). Addition of ESS (5%, 10% and 20%) to the SOF resulted in a significant increase in the cleavage rate of oocytes (73.79%, 73.25% and 77.61%) compared with the oocytes fertilized in SOF without ESS (0%, P<0.01), although there was no significant difference in the cleavage rate among the three ESS groups (P>0.05). Supplementing the fertilization medium containing 5% ESS with 5IU/ml heparin did not affect the cleavage rate of oocytes (86.63% vs. 86.64%), but the cleavage rate decreased significantly when the concentration of heparin was increased to 10IU/ml (75.53%, P<0.05). Moreover, addition of 3mg/ml bovine serum albumen (BSA) to the fertilization medium containing 5% ESS also did not affect the cleavage rate of oocytes at 48h after IVF (70.83% vs. 73.79%, P>0.05).In conclusions, (1) Follicle cutting is more effective than follicle aspiration in recovering COCs from ovine ovaries; (2) ESS from estrus ewes induced in anoestrus season can improve IVF efficiency of sheep oocytes matured in vitro; (3) Heparin and BSA are unnecessary for the IVF of ovine oocytes when fertilization medium contains ESS, and high concentration of heparin (10IU/ml) may play a negative role in the process of sheep IVF.