Follicle profile and plasma gonadotropin concentration in pubertal female ponies

Abstract

Twelve female ponies were examined daily for 30 days and classified as ovulating (OV; N = 6; 197 ± 6 kg) or prepubertal (PP; N = 6; 196 ± 9 kg). Follicles were detected by ultrasound and gonadotropins quantified by radioimmunoassay. The mean diameter of the largest follicles was significantly larger in OV (38 ± 1 mm) than in PP (26 ± 2 mm) but there was no difference between groups in the size of the second largest follicle. There were more small follicles (<24 mm) in the PP than in the OV group, but PP fillies had a smaller number of follicles >29 mm than the OV fillies. Follicle-stimulating hormone (FSH) levels did not differ between groups but PP fillies had lower luteinizing hormone (LH) peak (8 ± 1 ng/ml) and basal (4 ± 0.5 ng/ml) levels, lower peak magnitude (2 ± 0.2 ng/ml) and period average (5 ± 0.6 ng/ ml) than OV fillies (32 ± 4.5, 8 ± 1.2, 17.1 ± 6, and 15 ± 2.3 ng/ml, respectively). The PP group, in contrast to the OV group, showed no relationship between FSH surge and follicle wave emergence. We conclude that an LH concentration higher than 8 ng/ml is needed for follicle growth to a preovulatory size. Wave emergence and FSH secretion seem to be independent events, probably due to an inhibitory neural system in these PP animals. PP fillies may provide a physiological model for the study of follicle wave emergence which apparently does not depend on gonadotropin levels.

Circulating Pituitary and Gonadal Hormones in Spring-born Thoroughbred Fillies and Colts from Birth to Puberty

“…The reduction in gonadotropins and in turn steroids in the non-breeding winter months could be due to the modulatory role of decreased photoperiod and low hypothalamic GnRH output [29]. The HPG axis is regulated by the negative feedback of steroids on gonadotropins [7], which is difficult to appreciate in this study due to the long interval sampling procedure. However, colts and fillies in this study exhibited a clear increase in gonadotropins and concomitant gonadal steroid hormones during the second breeding season, which indicates that the animals reached puberty.…”

“…This variation can be attributed to differences in breeds [3][4][5], locales, management and puberty definition [6,7]. Furthermore, there have been few studies on Thoroughbreds [7][8][9], and most of them were conducted in southern hemisphere. Geographical location influences the season, and there have been fewer reports regarding puberty in horses from the northern hemisphere.…”

Follicular Dynamics in Pubertal Arab Mares during Spontaneous Estrus

“…The mean diameter of the largest follicles was significantly larger in ovulatory fillies (38 ± 1 mm) than in prepubertal (26 ± 2 mm) but there was no difference between groups in the size of the second largest follicle. There were more small follicles (<24 mm) in the prepubertal than in the ovulatory pony fillies group, but prepubertal fillies had a smaller number of follicles>29 mm than the ovulatory fillies (Nogueira 2004) In addition, the maximal diameter of the dominant follicle for secondary waves was significantly smaller than for primary waves and maximal diameter was reached earlier (mean maximal diameter of largest follicle: 37.2±1.0 and 45.8±1.0 roan, (Ginther 1993). Compared to pubertal fillies, the older the mares is the more likely to ovulate from smaller follicles.…”

“…In prepubertal and ovulating ponies, the largest follicle diameter during the 30-day period of the study was larger in the ovulating group than in the prepubertal group, but the diameter of the second largest follicle did not differ between groups. The daily difference between the largest and second largest follicles was higher for ovulating than prepubertal, also was the difference between the largest follicle diameters minus the diameter of the second largest follicle (Nogueira, 2004). The mean diameter of the largest follicles was significantly larger in ovulatory fillies (38 ± 1 mm) than in prepubertal (26 ± 2 mm) but there was no difference between groups in the size of the second largest follicle.…”

“…Recently, follicle profile was studied in ovulatory and non-ovulatory pubertal female pony (Nogueira, 2004). No data was available about follicular dynamics in pubertal fillies because native and Arabian mare's needs delicate handling during such study and younger inexperienced fillies to either rectal or ultrasound examination will need much more experience in both rectal and ultrasound examination, in addition to a suitable operator hand size to reach ovaries.…”