Seasonal variations of sex steroid hormones in follicular fluid, and their follicular morphologies in mares.

摘要

Ovaries containing a total of 194 follicles >10 mm in diameter were collected from 28 mares slaughtered in January, March, May, August and October at an abattoir in south-western Japan. Large follicles >40 mm in diameter and corpora lutea (determined by ultrasonography) were observed in ovaries collected in March, May and August, whilst they were absent in January. Ovaries collected in October had a corpora lutea but no large follicles. Follicular development were classified into 4 stages dependingon morphological findings (non-atretic, mild atretic, atretic and heavy-atretic). Most follicles were classified as atretic, while non-atretic large follicles >40 mm in diameter were observed only in ovaries collected in March to August. In October andJanuary, only medium-sized non-atretic follicles, 30-40 mm in diameter, were observed. Oestradiol-17beta and progesterone concentrations in follicular fluid decreased as the follicle became atretic. It is concluded that the breeding season had already started by March and continued until August, with some ovarian activity throughout the non-breeding season.