Number and density of equine preantral follicles in different ovarian histological section thicknesses.

Regardless of species, advances in preantral follicle culture and cryopreservation and transplant of ovarian tissue techniques are dependent on the number and density of preantral follicles in the ovary. This study tested the effect of different histological section thicknesses on number, classification, and density of equine preantral follicles. An ovarian fragment was obtained from 5- to 10-year-old mares (n = 14) after slaughter, and each fragment was submitted to three histological section thickness treatments: 3, 5, and 7 μm. The area (cm(2)) of each ovarian fragment was measured, and the sections were evaluated by light microscopy. The percentage of morphologically normal follicles (89%) was similar (P > 0.05) among primordial, transitional, and primary follicles and also among histological section thicknesses. A greater (P < 0.05) number of preantral follicles per histological section were seen in the 7-μm (8.0 ± 2.2) than that in the 3-μm (3.4 ± 0.7) treatment. Furthermore, a linear regression analysis reported that the number of preantral follicles increased (P < 0.05) when a thicker section treatment was used. However, no association (P > 0.05) between follicular density and treatment was observed. The mean number of preantral follicles per fragment (45.3 ± 18.8) and the follicular density (3.0 ± 0.5 follicles per cm(2)) were different (P < 0.05) among mares. In conclusion, this study on equine preantral follicles reported that (1) a 7-μm histological section thickness might be recommended because it allowed identification of a greater number of preantral follicles per sample, (2) a large individual variation in follicle population and density was detected regardless of histological section thickness, and (3) mares have a low number and density of preantral follicles when compared with those reported for other species.