Quantitative and qualitative analysis of the effectiveness of a mechanical method for the isolation of preantral follicles from ovine ovaries

The preantral follicles are the major source of oocyees and its utilization has been investigated as an important tool to store large numbers of female gametes for further utilization in reproductive programs. The aim of the present study was to perform quantitative and qualitative analyses of the efficacy of a mechanical method for isolating of preantral follicles from the ovaries of fetuses and from nonpregnant and pregnant ewes, using as reference the population of preantral follicles in situ. In the isolation method the ovaries were cut into fragments in the tissue chopper. Then, the suspension was filtered through nylon mesh filters. The number of isolated follicles per ovary was 1655, 4735 and 4770, respectively, for the fetus, nonpregnant ewe and pregnant ewe. The number of in situ preantral follicles per ovary was 32961, 16627 and 17794, respectively, for the fetus, nonpregnant ewe and pregnant ewe. The follicle recovery rate (number of isolated preantral follicles/number of in situ preantral follicles x 100) was higher in adult ewes (26 and 28%, respectively, for nonpregnant and pregnant ewes) than in fetuses (5%). Histological analysis showed that very few preantral follicles (less than 0.26% in situ and 0.46% after the isolation procedure) were degenerated. In conclusion, this study showed that a mechanical method could be used effectively to isolate a large number of intact ovine preantral follicles. In the future, with improvements in culture systems, the isolation of a great number of oocytes enclosed in preantral follicles will make a valuable contribution to the rare breeds and endangered species, agricultural efficiency and basic research in folliculogenesis. (C) 2000 by Elsevier Science Inc.