Miniature ponies: 2. Endocrinology of the oestrous cycle

Abstract

Plasma concentrations of FSH, LH, oestradiol and progesterone were studied daily during 12 interovulatory intervals and 21 periovulatory periods in nine Miniature ponies. The peak of the FSH surge that was temporally associated with emergence of the future ovulatory follicle occurred when the follicle was approximately 9 mm, compared with a reported diameter of 13 mm in larger breeds. The ovulatory LH surge involved a slow increase between Days 13 and 18 (ovulation=Day 0; 0.6+/-0.1 ng day(-1)), a minimal increase or a plateau on Days 18 to 21 (0.04+/-0.1 ng day(-1)), and a rapid increase after Day 21 (2.2+/-0.4 ng day(-1); P<0.0001). The end of the plateau and the beginning of the rapid increase occurred on the day of maximum concentration in the oestradiol preovulatory surge. An unexpected mean increase and decrease in LH occurred (P<0.04) on Days 5 to 9. Concentrations of oestradiol and progesterone seemed similar to reported results in larger breeds. Results indicated that in Miniature ponies the peak of the FSH surge associated with emergence of the future ovulatory follicle occurred at a smaller diameter of the future ovulatory follicle than in larger breeds, the ovulatory LH surge increased in three phases, and the ovulatory LH surge was followed by an LH increase and decrease during the early luteal phase.

A Review of the Estrous Cycle and the Neuroendocrine Mechanisms in the Mare

“…The estrous cycle is defined as the interval of time between two consecutive ovulations. The approximate length varies between 18 and 22 days, considering on average a period of 21 days [18,19]. The current nomenclature stipulates that the estrous cycle consists of two clearly differentiated stages: estrus or follicular phase and diestrus or luteal phase.…”

“…Thus, estrus is extended in autumn (7-10 days) and is shortened considerably, in late spring and early summer (4-5 days). During this period the mare is sexually receptive to the stallion genital tract and is ready to receive and transport of sperm and finally culminates with ovulation [8,19,20].…”

“…Ovarian ultrasound shows a variable number of follicles from anechogenic consistency that can vary in size according to the time of development [8,18,19,41,48]. Preovulatory follicle exhibits pronounced morphological changes, varying spherical or pear-shaped to conical in 84% of the pre-ovulatory period while the remaining follicles maintained the spherical shape [12].…”

Some aspects of peripartum, neonate and foal heat in mini pony mares

“…North Pomfret, VT: Trafalgar Square Publishing. Gastal E. L., A. P. Neves, R. C. Mattos, B. P. L. Petrucci, M. O. Gastal and O .J. Ginther (2008) Miniature ponies: 1.…”

“…Studies in miniature mares have fundamental and practical importance for formulating and testing hypothesis of physiological events, allowing precise diagnosis and treat-ments in reproductive practice. Although there are a few clinical reports in miniature mares (Judd 1994, Tibary 2004, detailed scientific studies were only performed recently on follicular, luteal, and endometrial dynamics (Gastal et al 2008) and also endocrinology (Ginther et al 2008) during the estrous cycle. The physiological aspects of the peripartum and neonatal period are well studied in the Thoroughbred breed (Koterba et al 1990, Kurtz Filho 1995.…”