Induction of Ovulation and Multiple Ovulations in Seasonally Anovulatory and Ovulatory Mares with an Equine Pituitary Extract

Abstract

A crude equine pituitary extract (EE) was used to induce single and multiple ovulations in seasonally anovulatory pony mares. Six control mares received saline vehicle only. Twelve mares were injected daily for 14 days with a total of 6.6 mg/kg body weight of EE (3.3 U NIH-FSH-S1). Six of the EE-treated mares were also treated with HCG (2,000 IU) on day 13, bred on days 13 and 15, and necropsied on day 17. The ovarian follicles were ≤10 mm in diameter at the beginning of treatment. The number of mares ovulating/group and the number of ovulations/mare were significantly greater following EE or EE+HCG than following saline vehicle administration (5/5, 1.6; 6/6, 1.8; 0/6, 0, respectively). The interval from day 13 (day of HCG treatment) to day of first subsequent ovulation was shorter (P<.05) in EE+ HCG-treated mares (2.3 days) than in EE-treated mares (4.4 days). A total of six fertilized and two recent, non-fertilized ova was recovered. A second experiment was designed to determine if EE treatment could induce multiple ovulations in seasonally ovulatory mares. Twenty-one cycling pony mares were assigned randomly to three groups (seven/group): 1) non-treated controls, 2) treatment during diestrus beginning on day 11 post-ovulation, and 3) treatment beginning on day one of estrus. Treated mares were given a total dose of 4 mg/kg body weight of EE (2 U NIH-FSH-S1) divided into six equal, daily subcutaneous injections. Number of mares with more than one ovulation was greater (P<.05) for mares in which treatment was initiated on day 11 post-ovulation (4/7) or on day 1 of estrus (3/7) than for controls (0/7). There were fewer (P<.01) mares showing estrus during the first post-treatment ovulatory period when mares were treated during diestrus compared to control mares (3/7, 7/7, respectively). Three of the mares that did not show estrus had multiple ovulations and one mare did not ovulate. There was a greater (P<.05) number of follicles ≥25 mm on the day of the first post-treatment ovulation when mares were treated during diestrus (3.2) or estrus (2.4) than when mares were untreated (0). Results of experiment 1 confirmed that EE can induce ovulation in mares during the anovulatory season and indicated that timing of ovulation can be improved with HCG and that ova from induced ovulations are fertilizable. Results of experiment 2 demonstrated that EE can induce follicular activity and multiple ovulations during the ovulatory season. Copyright © 1977. American Society of Animal Science . Copyright 1977 by American Society of Animal Science.