Lowering storage temperature during ovary transport is beneficial to the developmental competence of bovine oocytes used for somatic cell nuclear transfer

The objective of this study was to determine the effect of storage temperature during ovary transport on the developmental competence of bovine oocytes for use in somatic cell nuclear transfer (SCNT). Ovaries obtained from a slaughterhouse were stored in physiological saline for 3-4 h at one of the three temperatures: 15 degrees C, 25 degrees C, or 35 degrees C. The developmental competence of oocytes used for SCNT was ascertained by cleavage and blastocyst formation rate, total cell number, apoptosis index, and the relative abundance of Bax and Hsp70.1 in day 7 blastocysts. Ovaries stored at 35 degrees C for 3-4 h reduced the recovery rate of grade land II oocytes compared with those stored at 25 degrees C or 15 degrees C (45.1 +/- 0.7% vs. 76.7 +/- 1.2% or 74.8 +/- 2.0%, P < 0.05). The proportion of oocytes matured to the Mil stage (maturation rate) for oocytes stored at 35 degrees C was significantly lower than those stored at 25 degrees C or 15 degrees C (51.3 +/- 0.9% vs. 75.1 +/- 1.4% or 71.7 +/- 1.3%, P < 0.05). Cleavage rate (77.7 +/- 2.1%, 77.9 +/- 1.1% and 72.1 +/- 0.7% for 15 degrees C, 25 degrees C and 35 degrees C groups, respectively) and blastocyst formation rate (39.1 +/- 0.5%. 36.8 +/- 1.4% and 32.2 +/- 0.9% for 15 degrees C, 25 degrees C and 35 degrees C groups, respectively) following SCNT were not significantly different between treatments. Oocytes from ovaries stored at 15 degrees C, however, produced blastocysts with higher cell numbers (97.3 +/- 8.6 vs. 80.2 +/- 10.8 or 77.4 +/- 11.7; P < 0.05) and lower apoptotic index (5.1 +/- 1.3 vs. 13.5 +/- 1.6 or 18.6 +/- 1.1, P < 0.05) than those stored at 25 degrees C or 35 degrees C. The relative abundance of Bax and Hsp70.1 in day 7 blastocysts produced from oocytes derived from ovaries stored at 15 degrees C was lower than those stored at 25 degrees C or 35 degrees C (P < 0.05). It was concluded that a storage temperature of 15 degrees C for a 3-4 h period had a significant beneficial effect on the quality and developmental competence of oocytes used for SCNT due to the alleviation of stresses on the oocytes compared with those subjected to storage temperatures of 25 degrees C or 35 degrees C. (C) 2011 Elsevier B.V. All rights reserved.