The Influence of Season on Estrus, Ovulation, and Reproductive Hormone Secretions in Barren and Periparturient Pony Mares (Postpartum, Adrenal, Parturition)
Pope, Nancy Salka
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https://hdl.handle.net/2142/70023
Description
Title
The Influence of Season on Estrus, Ovulation, and Reproductive Hormone Secretions in Barren and Periparturient Pony Mares (Postpartum, Adrenal, Parturition)
Author(s)
Pope, Nancy Salka
Issue Date
1984
Department of Study
Animal Science
Discipline
Animal Science
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Biology, Animal Physiology
Abstract
An extended study was done to determine reproductive and hormonal parameters in pony mares during the peripartum period over three seasons: winter, summer and fall. Experiments were also conducted on control and hormonally manipulated barren mares during the same three seasons.
Blood samples were obtained on a daily and frequent basis from foaling mares prepartum, during parturition and postpartum. Estrous behavior and ovulation parameters were also obtained. Progesterone:estradiol ratios were found to be decreasing at the time of parturition. A surge in LH was found to occur soon after the precipitous decline in progesterone seen at parturition. Androstenedione levels were elevated during parturition. LH pulsatile release on days 1, 4, 7 and 10 postpartum is described. Greater than 90% of mares showed ovulation within 20 days postpartum regardless of season.
Treatment of barren mares with 10 daily progesterone injections with PGF(,2)(alpha) on day 7 and hCG on day 2 of estrus following progesterone withdrawal was done. One group received LH/FSH injections in addition to the treatment beginning on day 9 of progesterone and continuing until estrus was detected. In winter, the gonadotropin-treated group showed more ovulations than controls or the group treated without gonadotropins. Seasonal differences in androgen levels during vehicle injections of controls were very evident, possibly a stress-related response. Dexamethasone was shown to decrease testosterone and androstenedione levels in mares without affecting estradiol, progesterone or LH, and to abolish estrous behavior in intact mares during the winter.
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