[Effect of storage temperature of ovaries on in vitro maturation, fertilization and cleavage of bovine oocytes]

A total of 697 ovaries were obtained in 5 batches (replicates) from a local slaughter-house and distributed at random into 2 groups: group 1) Ovaries stored at 4C(n=318); group 2) ovaries stored at 38C (n=379). After a storage of 5 hrs at these temperatures, the ovaries and oocytes were manipulated at 38C. All oocytes were cultured in TCM-199, with 10% heat-inactivated fetal calf serum (FCS) and 0.02 mg/ml of follicle stimulating hormone, for 24 hr under 5% CO2 air atmosphere (in vitro maturation). The oocytes were then co-cultured for 6 hr with frozen/thawed epididymal spermatozoa, from one bull, capacitated by a preincubation method (Brackett and Oliphant, 1975). The oocytes were again then cultured for 18 and 48 hr in TCM-199 with 10% FCS to determine the rate of fertilization and cleavage (2-8 cells). Of the 1368 oocytes collected (group 1: 634 and group 2: 734), 760 (56%) were selected for culture (group 1: 370 and group 2: 390). The mean number of oocytes recovered per ovary (group 1: 2.0 and group 2: 1.9) and the rate of oocytes selected for culture (group 1: 370/634; 58.4% and group 2: 390/734; 53.1%) were not different between the groups. Furthermore there were no differences (p 0.05) between groups on rate of penetration (group 1: 36/49; 73.5% and group 2: 30/42; 71.4%), fertilization (group 1: 27/49; 55.1% and group 2: 28/42; 66.6%) and development (group 1: 127/241; 52.7% and group 2: 163/269; 60.6%). The rate of oocytes that cleave 2-4 cells (group 1: 102/241; 42.3% and group 2: 124/269; 46.1%) and 4-8 cells (group 1: 25/241; 10.4% and group 2: 39/269; 14.5%) was not different between groups. Conversely, polyspermy was higher (p 0.05) in group 1 (9/36, 25.0%), than in group 2 (2/30; 6.6%). These results indicate that cattle ovaries can be stored at 4C for at least 5 hr, without reducing the capacity of the oocytes to be fertilized and developed in vitro up to the 2-8 cell stage