Effects of incubation temperature and bicarbonate on maturation of pig oocytes in vitro.

Pig oocytes cultured at 39 degrees C had a higher percentage of polar body formation than did those cultured at 37 degrees C. A culture medium based on Medium 199 with Earle's salts and supplemented with 15% serum from a young castrated boar was just as good as the same formulation containing additional pyruvate, lactate and insulin, and superior to a modified Krebs-Ringer bicarbonate medium. When the bicarbonate buffer system (Earle's salts) of Medium 199 was replaced with a phosphate buffer system (Hank's salts), the rate of polar body formation was decreased. When the Hank's based medium was supplemented with a bicarbonate buffer system, polar body formation was restored to the level in Earle's based medium. This suggests that CO2/bicarbonate may be important for the normal maturation of pig oocytes.