Plasma luteinzing hormone, progestogens, and estrogens in mares during gestation, parturition, and first postpartum estrus (foal estrus)
Noden, P.A.; Oxender, W.D.; Hafs, H.D.
American Journal of Veterinary Research 39(12): 1964-1967
1978
ISSN/ISBN: 0002-9645 PMID: 749581 Document Number: 135827
The length of gestation in six mares averaged 332 plus or minus 3 days. During gestation two major changes occurred in hormonal dominance. LH activity increased from 20- to 200-fold above basal (40 ng/ml) concentrations in the 2nd to the 5th months. This increase in LH activity appeared to be due primarily to PMS. Plasma oestrogens increased from basal concentrations (6 to 12 pg/ml) during the 1st trimester to 426 plus or minus 102 pg/ml near the end of the 2nd trimester and remained increased until near parturition. Progestogen concentrations remained relatively stable during gestation. Starting 48 hours before parturition, concentrations of oestrogens and progestogens decreased sharply to 25.8 plus or minus 3.9 pg/ml and 3.3 plus or minus 0.9 ng/ml respectively, on the day of parturition. Plasma LH concentrations remained unchanged at parturition, increased on the 3rd day after parturition to 253 plus or minus 32 ng/ml, and remained increased until after ovulation. Foal oestrus began 6.5 plus or minus 0.4 days and ovulation occurred 12.3 plus or minus 0.6 days after parturition. Progesterone concentrations averaged near 1.0 ng/ml during foal oestrus and then increased after ovulation.