EFFECTS OF TEMPERATURE-GRADIENTS ON IN-VITRO MATURATION OF BOVINE OOCYTES

The effect of temperature gradients on in vitro maturation of bovine o ocytes was examined in this study. Six treatment groups were made by c ombining 3 different maturation periods (0 to 10 h, 10 to; 18 h and 18 to 24 h) with 2 different culture temperatures (37.0 degrees C and 38 .5 degrees C). The frequency of oocytes matured to the metaphase II st age was apparently gradually increased as the culture temperature was increased from 37.0 degrees C to 38.5 degrees C at 0, 10 and 18 h afte r the onset of culture (75.2 vs 80.5, 82.3 and 84.3%, respectively), b ut this difference was not significant. Neither was the minor decrease in the proportion of oocytes reaching metaphase II when the temperatu re was decreased from 38.5 degrees C to 37.0 degrees C at 10 and at 18 h after the onset of maturation (84.3 vs 82.4 and 78.0%, respectively ). However, more oocytes cleaved (79.2%; P = 0.0653) and developed to morulae (43.6%; P = 0.0019) and blastocysts (27.4%; P = 0.1568) when t hey were in vitro matured at 38.5 degrees C between 0 and 10 h, and th en at 37.0 degrees C from 10 to 24 h. Although only the morula group w as statistically different, cleavage- (79.2 vs 69.8, 72.5, 74.2, 76.3, 74.3%, respectively) and blastocyst formation (27.4 vs 23.2, 24.6, 25 .2, 19.6, 21.9%, respectively) from this group was the highest among t he 6 treatments. (C) 1998 by Elsevier Science Inc.