Macroscopic classification of bovine follicles and its validation by micromorphological and steroid biochemical procedures.

Bovine antral follicles ranging between 2 and 20 mm in diameter were dissected free of stromal tissue and classified under a stereomicroscope using criteria similar to those of Moor et al. (1978). For light-microscopic evaluation of the macroscopic classification, 191 follicles were fixed in Bouin's fluid, embedded in paraffin, sectioned through the cumulus and oocyte and stained with haematoxylin-eosin. To study the relation between the macroscopically determined morphological characteristics and the oestradiol-17 beta (E2) level in the follicular fluid (FF), 39 follicles of one animal were selected. The E2 level, expressed as pmol/ml of FF, was estimated by RIA. The overall correlations between macroscopic classification and histological qualification of non-atretic and atretic follicles were 93.3 and 95.5 p. 100, respectively. Furthermore, the results indicated that the E2 level of small non-atretic follicles was lower than that of larger follicles and that the level in the FF decreased with increasing degeneration. It is concluded that macroscopic criteria offer a highly reliable means of identifying bovine follicles in terms of both micromorphology and functionality.