Quantitative and qualitative analysis of the effectiveness of a mechanicalmethod 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 femal e gametes for further utilization in reproductive programs. The aim of the present study was to perform quantitative and qualitative analyses of the e fficacy of a mechanical method for isolating of preantral follicles from th e ovaries of fetuses and from nonpregnant and pregnant ewes, using as refer ence the population of preantral follicles in situ. In the isolation method the ovaries were cut into fragments in the tissue chopper. Then, the suspe nsion was filtered through nylon mesh filters. The number of isolated folli cles per ovary was 1655, 4735 and 4770, respectively, for the fetus, nonpre gnant ewe and pregnant ewe. The number of in situ preantral follicles per o vary was 32961, 16627 and 17794, respectively, for the fetus, nonpregnant e we and pregnant ewe. The follicle recovery rate (number of isolated preantr al follicles/number of in situ preantral follicles x 100) was higher in adu lt ewes (26 and 28%, respectively, for nonpregnant and pregnant ewes) than in fetuses (5%). Histological analysis showed that very few preantral folli cles (less than 0.26% in situ and 0.46% after the isolation procedure) were degenerated. In conclusion, this study showed that a mechanical method cou ld be used effectively to isolate a large number of intact ovine preantral follicles. In the future, with improvements in culture systems, the isolati on of a great number of oocytes enclosed in preantral follicles will make a valuable contribution to the rare breeds and endangered species, agricultu ral efficiency and basic research in folliculogenesis. (C) 2000 by Elsevier Science Inc.