Symposium on Reproduction, September 6-7, 1973, School of Veterinary Medicine, University of California, Davis : sponsored by American Veterinary Society for the Study of Breeding Soundness, American College of Theriogenologists, School of Veterinary Medicine, University of California, Davis.

  • Symposium on Reproduction (1973 : Davis, Calif.)
Date:
[1973?]
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Licence: Attribution-NonCommercial 4.0 International (CC BY-NC 4.0)

Credit: Symposium on Reproduction, September 6-7, 1973, School of Veterinary Medicine, University of California, Davis : sponsored by American Veterinary Society for the Study of Breeding Soundness, American College of Theriogenologists, School of Veterinary Medicine, University of California, Davis. Source: Wellcome Collection.

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    2 The Ш rise begins at approximately the time regression of the carpus lutem is corplete, or vdien progestin levels have declined to less than 1 ng/lnl plasma. Another of expressing this is, 3 days follcwing the beginning of corpus luteum regression. Ovulation occurs approximately the third d^ of the LH rise, or on about the 4th or 5th day of estrus. Not only is there sustained rise prier to ovulation, but LH continues to rise several days postovulaticn. The reason for this sustained LH peak is not known. One main reason may be that it may have a long half-life. Par lav has found the half-life of most gonadotrcphins in the rat to be a matter of minutes, viiereas the half-life of equine LH and PMSG in the rat are a matter of days. The physiological reason for this broad LH peak is not ^>parent. Whether or not LH has anything to do vàth follicular grwtli remains to be proven. Pattison et al. have reported an estrogen вглгде that slightly precedes the LH surge. Considerable follicular development occurs prior to ovulation in regard to the nimber of follicles developed, which leads us to the se¬ cond point; The mare has a high percentage of multiple ovulations—^proximately 25% in our experience—in lieu of the fact that only about 1% of births involve live twin foals. The mare seems incapable, as a rule, in develop¬ ing two or more zygotes to term; yet she is often involved in multiple ovulations. The next slide [Slide #4] shows the time intervals observed for mvilti- ple ovulations. As can be seen in the slide, most ovulations occur within 24 hours of each other. The formation of two corpora lutea during the estrous cycle of the mare apparently does not result in higher levels of progesterone in