Reproduction Abstracts

Antral follicle waves in mares are considered a model for ovarian function in women, and can be sampled with relative ease in vivo or following ovary removal to investigate the regulation of follicle growth. To begin determine the effects of disease which may dysregulate follicular granulosa (GC) or theca cell (TC) proliferation, this study characterised 41 antral follicle wall H&E sections recovered from ovaries of 16 mares that were classified as healthy or suffered from chronic mild or severe clinical disease.

Follicles measured on average 21 mm in diameter which was unaffected (P>0.05) by disease status, and were allocated to very healthy (VH), healthy (H), early atretic (EA) and late atretic (LA) categories based on the histological appearance of the GC and TC layers. Disease status had no influence on the follicle category (P>0.05), and did not alter percentages of basal, intermediate or antral GC, or GC layer thickness (P≥0.3). However, the TC layer thickness was increased (P<0.01) in follicles from mares with severe disease compared with healthy mares. More healthy than diseased mares were in seasonal transition at ovary recovery (P<0.05), and transitional follicles showed reduced (P<0.05) TC layer thickness and percentages of basal GC and large TC, compared with follicles recovered in deep anoestrus.

Follicle categorization into VH, H or EA did not alter any GC layer characteristics (P>0.05), but H follicles had a thicker TC layer than EA follicles (P<0.05). In LA follicles the GC layer had disappeared, and the percentage of large TC was reduced, while the percentage of small TC was increased compared to VH and H follicles (P<0.001), reducing the TC layer thickness in LA versus H follicles (P<0.05).

In conclusion, basic histomorphological GC and TC measurements in equine large antral follicles appear more influenced by season and follicle atresia than by disease.