Effect of time during transport of excised mare ovaries on oocyte recoveryrate and quality after in vitro maturation

In the mare only a limited number of oocytes can be successfully collected in vivo,so that when large numbers of oocytes are needed for experimentatio n, ovaries harvested front slaughtered mares must be used. The resulting te mperature changes and time intervals mandated by handling and transport of ovaries from the slaughterhouse to the laboratory adversely affect the rate of oocyte recovery and their quality after IVF and maturation. We chose to study the effect of temperature and time in transit of excised ovaries by evaluating rate of oocyte recovery, nuclear maturation stage rea ched before, and cleavage rate reached after IVF, following short (1.5 to 4 h) and long (6 to 8 h) storage. Temperatures in the storage container decr eased from 37-C to 32 degrees and 27.5 degrees C during the short and long interval, respectively. The cumulus-oocytes complexes (COCs) were classifie d as having a compact cumulus, completely or partially surrounding the oocy te (compact); those having only a corona radiata surrounding the oocyte (co rona); those having a completely or partially expanded cumulus, showing a c ellular or sparsely cellular, gelatinous cloud around the oocyte (expanded) ;and those that were completely denuded of both cumulus and corona cells (d enuded). All COCs, except the denuded ones, which were discarded, were matu red in vitro for 30 h at 38.5 degrees C in 5% CO2. The recovery rate of ooc ytes was significantly higher after long vs short storage (48 vs 35%; P < 0 .01), but the distribution of the collected COCs into the 4 classes was not affected by the storage time. After in vitro maturation nuclear maturity w as not affected by the storage time, but oocytes with intact cytoplasmic me mbranes were more frequently found after short than after long storage (54 vs 34%; P = 0.07), and fully matured oocytes were more often seen with inta ct membrane (P < 0.01). Moreover, oocytes with intact membranes in metaphas e II (MII) were associated with short storage intervals and the corona COC class, while damaged membranes and incomplete maturation were associated wi th the long storage and the compact COC class. (C) 1999 by Elsevier Science Inc.