Miniature ponies: 1. Follicular, luteal and endometrial dynamics during the oestrous cycle.

Follicular dynamics were studied during 12 interovulatory intervals (IOIs) and 36 preovulatory periods in Miniature mares. The percentage of IOIs with the following follicle events was: ovulatory wave with only one follicle >= 10 mm (55%), diameter deviation similar to previous reports in larger mares (25%) and minor waves emerging before or after the ovulatory wave (55%). Follicle data were compared among Miniature ponies, large ponies and Breton horses (n = 12 IOIs per breed). The IOI was longer (P < 0.001) in Miniature ponies (23.3 +/- 0.9 days) and in large ponies (23.9 +/- 0.5 days) than in Breton horses (20.3 +/- 0.7 days). The Miniature ponies had fewer (P < 0.0001) growing follicles >= 10 mm per ovulatory wave (1.5 +/- 0.3) and more (P < 0.0004) ovulatory waves (6/11) with only one follicle >= 10 mm than large ponies (9.8 +/- 0.8 and 0/12) and horses (5.8 +/- 0.9 and 0/12). Maximum diameter of the preovulatory follicle was smaller (P < 0.003) in the Miniature ponies (38.3 +/- 0.7 mm) than in the horses (44.5 +/- 1.4 mm), but the difference between breeds was slight (6%) compared with the difference in bodyweight (65%). Considering the small number of follicles per ovulatory wave, Miniature mares are a potential model for comparative studies in folliculogenesis within and among species.