J. Anim Sci.
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J. Anim Sci. 1988. 66:98-103.
© 1988 American Society of Animal Science
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Follicular Growth and Estradiol Influence on Luteal Function in Mares

S. S. King1 and J. W. Evans2

University of California, Davis 95616

Abstract

Follicular growth, circulating estradiol concentrations and endometrial prostaglandin F2{alpha} (PGF2{alpha}) production were measured to determine whether there is an interrelationship among these factors associated with luteolysis. Follicular growth was monitored by rectal palpation every other day during diestrus in 16 mares. Plasma estradiol was determined for daily samples during all estrous cycles. Endometrial tissue was removed for PGF2{alpha} analysis by radioimmunoassay on d 10, 12, 14 or 16 during several normal cycles and after d 30 during spontaneously prolonged cycles. Circulating estradiol concentrations were highly correlated with follicular diameter. Follicular growth was initiated before d 14 in normal cycles, thus estradiol was significantly elevated during the portion of diestrus prior to luteolysis. This was not the case during spontaneously prolonged cycles in which a) there was no correlation between follicular size and circulating estradiol, b) follicular growth was initiated an average of 19 d postovulation, and c) estradiol concentrations did not increase. Diestrous estradiol concentrations, during normal cycles, were significantly elevated immediately (72 to 24 h) prior to the time at which peak endometrial PGF2{alpha} production occurred (d 12 and 14). During spontaneously prolonged cycles, estradiol concentrations did not rise at the time of expected luteolysis, and endometrial PGF2{alpha} production was minimal in d 30 biopsies. Results suggest that diestrus follicular growth and its consequent estradiol production may play a role in initiating luteolysis through endometrial PGF2{alpha} production and that delay or failure of this process may result in spontaneously prolonged corpora luteal function.

Footnotes

1 Current address: Southern Illinois Univ., Carbondale 62901.

2 Current address: Texas A&M Univ., College Station 77840.






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