Prostaglandin F-induced estrus in ewes exhibiting estrous cycles of different duration

Horacio Cárdenas, Todd M. Wiley, William F. Pope*

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

3 Scopus citations


Effects of prostaglandin F (PGF), administered during the mid-luteal phase of the estrous cycle, were examined in ewes exhibiting estrous cycles classified as short (≤16.5 days, short-cycle ewes, n=10) or long (≥18 days, long-cycle ewes, n=9) based on the durations of two estrous cycles (cycles -2 and -1) before treatment. The ewes received (i.m.) 20 mg of PGF on day 10 of the third estrous cycle (cycle 0) followed, 36 h later, by 25 μg of gonadotropin releasing hormone (GnRH) to time the events of ovulation. Duration of subsequent estrous cycles +1 and +2 were recorded, and then the ewes were treated with the same combination of PGF and GnRH beginning on day 10 of estrous cycle +3. Ovaries were recovered 6 h after GnRH administration to assess development of pre-ovulatory follicles. The proportion of ewes that exhibited estrus after PGF and GnRH treatment on cycle 0 was not different (P>0.05) between short- and long-cycle ewes. Onset of estrus occurred sooner (P<0.05) after PGF injection in short-cycle ewes than in long-cycle ewes (1.9±0.1 days and 2.3±0.1 days, duration of cycle 0 was 11.9 and 12.3 days, respectively). Duration of estrous cycle +1 was 1.2 days longer (P<0.01) than cycle -1 in short-cycle ewes. However, duration of estrous cycle +1 did not change (P>0.05) after PGF and GnRH administration in ewes having long cycles. Pre-ovulatory follicles did not differ (P>0.05) in numbers, diameter, layers of granulosa cells nor concentrations of progesterone and estradiol-17β in follicular fluid between short- and long-cycle ewes after PGF and GnRH treatment. In conclusion, ewes having short or long estrous cycles responded differently to PGF and GnRH treatment with respect to the interval to onset of estrus and duration of the subsequent estrous cycle.

Original languageEnglish (US)
Pages (from-to)123-129
Number of pages7
Issue number1-2
StatePublished - Jul 2004


  • Estrous cycle
  • Follicle
  • Ovary
  • PGF
  • Sheep

ASJC Scopus subject areas

  • Small Animals
  • Food Animals
  • Animal Science and Zoology
  • Equine


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