Predicting Ovulation in the Mare on the Basis of Follicular Growth and Serum Oestrone Sulphate and Progesterone Levels

Abstract

Summary Follicular growth and hormone determinations were used to predict ovulation in the mare. Thirty Finnhorse mares were used for the investigation and 38 oestrous cycles were studied. The mares were examined by rectal palpation and ultrasonography every 6 hours during late oestrus. Daily blood samples were obtained for progesterone and oestrone sulphate determination. The preovulatory follicle grew 3 mm a day up to 2 days before ovulation. The size then remained constant, before diminishing by 2–3 mm during the last 12 hours. The maximal diameter of the follicle was 43 ± 4 mm. In 89 % of the follicles the round shape became more irregular before ovulation. During the last 24 hours before ovulation 37 of 38 follicles were regarded as mature on rectal palpation. The oestrone sulphate level was highest 24–48 hours before ovulation, the first decrease being observed most commonly around ovulation (± 1 day). The size of the follicle was the most reliable criterion in the prediction of ovulation. Zusammenfassung Vorhersage der Ovulation bei der Stute aufgrund des Follikelwachstums, der östronsulfat‐ sowie der Progesteronkonzentration des Serums Zur Vorhersage der Ovulation wurden bei der Stute das Follikelwachstum sowie Hormonbestimmungen herangezogen. Für die Untersuchungen wurden 30 Stuten verwendet. Insgesamt wurden 38 Brunstzyklen untersucht. Die Stuten wurden während der späten Phase des östrus alle 6 Stunden mittels rektaler Palpation und Ultraschall untersucht. Für die Progesteron‐ und östronsulfatbestim‐mungen wurde täglich Blutproben entnommen. Der präovulatorische Follikel wuchs bis 2 Tage vor der Ovulation 3 mm pro Tag. Die Größe blieb dann konstant, bevor sich der Follikel in den letzten 12 Stunden um 2–3 mm verkleinerte. Der maximale Follikeldurchmesser betrug 43 ± 4 mm. Bei 89% der Follikel wurde die runde Form vor der Ovulation unregelmäßig. Bei rektaler Palpation wurden während der letzten 24 Stunden vor der Ovulation 37 von 38 Follikeln als reif beurteilt. Der östronsulfatspiegel war 24–48 Stunden vor der Ovulation am höchsten; die erste Abnahme wurde gewöhnlich um die Ovulation herum (± 1 Tag) beobachtet. Die Follikelgröße war für die Vorhersage der Ovulation das verläßlichste Kriterium.

Relationships of changes in B-mode echotexture and colour-Doppler signals in the wall of the preovulatory follicle to changes in systemic oestradiol concentrations and the effects of human chorionic gonadotrophin in mares

“…The absence of a mean diameter increase during the 36 h before ovulation in the controls is consistent with a previous report (Koskinen et al 1989) that mean diameter increased until 2 days before ovulation and remained constant thereafter. During the preovulatory period when mean diameter was no longer increasing in the controls, mean oestradiol concentrations were decreasing.…”

Ovarian Follicular Dynamics during the Estrous Cycle in Jennies in Upper Egypt

“…The growth rate of the ovulatory follicle between days −6 and −3 was greater than between days −3 and −1 for Jennies. The reduction in growth rate of the ovulatory follicle between maximum diameter (1 or 2 days before ovulation) and ovulation in Miniature ponies is consistent with what has been reported for Catalonian Jennies [15], larger ponies [29] and horses [24, 25, 27, 30, 31]. It was mentioned that the maximum diameter was attained on day −2 (46%) or day −1 (54%), reflecting the mean diameter decrease before ovulation [27].…”

Abnormal Reproductive Patterns in Przewalski's Mares Are Associated with a Loss in Gene Diversity1

“…By comparison, serum estrogen in the domestic mare peaks 2 days before ovulation, but among-animal variation is also reported to be high [30]. Species differences in timing of the preovulatory estrogen peak may be an artifact of the time lag (.24 h in the horse) between the secretion of estrogen in blood circulation and the excretion of its metabolites in voided urine [31].…”

“…In many ungulate species, such as the cow, ewe, and sow, the period of estrus is short (15,30, and 50 h, respectively [28]). However, in the domestic horse, estrogens increase during a period of at least 5 days coincidentally with follicular growth [10,25].…”